National Measurement (Recognized-Value Standard of Measurement of the Density of Water) Determination 2026

The central concept is the Recognized-Value Standard of Measurement, which is defined in the National Measurement Act 1960. This instrument creates a standard for a specific physical quantity: the density of water, expressed in kilograms per cubic metre. Density is not a base unit of measurement under the International System of Units (SI); it is a derived quantity. By declaring a recognised-value standard for this derived quantity, the instrument provides a legally enforceable reference for any subsequent measurement that depends on water density. The instrument operates by specifying three main components. First, at standard atmospheric pressure of 101,325 Pa and at any integer or half-integer temperature listed in Schedule 1, the density takes the value stated in that table. Second, for temperatures between the listed values at standard pressure, the density is to be obtained by linear interpolation between the two nearest entries in the table. This is a mandatory method; the instrument does not allow any more refined interpolation technique. Third, when the pressure of the water is not 101,325 Pa, the density at standard pressure (whether from the table or by interpolation) must be algebraically increased by a pressure correction term. That term is expressed as: (5.0619 − 0.0309 × t + 0.0003614 × t²) × 10⁻⁷ × (p − 101325). The temperature t is in degrees Celsius and the pressure p is in pascals. The correction can be positive or negative depending on whether p is above or below standard pressure. The instrument also introduces the concept of a tolerance statement or uncertainty statement. Clause 6(1)(d) provides that if the temperature used does not differ from the true mean temperature by more than 0.1 °C, if the pressure used does not differ from the true mean pressure by more than 1,000 Pa, and if impurities in the water do not exceed 1 part in 10⁵ by mass, the chance is not more than one in one hundred that the density so ascertained differs from the true value by more than 0.05 kg·m⁻³. This is a statement of the legal reliability of the standard, expressed in probabilistic terms. It does not define a permissible tolerance for enforcement purposes but rather defines the conditions under which the standard is considered to be accurate within a given confidence interval. The instrument adopts temperature in degrees Celsius, pressure in pascals, and mass fraction for impurities. The density formula itself is a rational function of temperature with a quadratic numerator and a rational denominator. The formula is given for information but the legal values are those in the table and those derived by linear interpolation and pressure correction. The table covers 0.0 °C to 40.0 °C in 0.1 °C increments, for a total of 401 data points. The density peaks near 3.98 °C at 999.972 kg·m⁻³, which is consistent with the well-known density maximum of water near 4 °C. The instrument does not define what constitutes water for this purpose beyond the impurity limit. It does not specify whether the water must be distilled, deionised, or otherwise treated, though the impurity limit of 1 part in 10⁵ by mass provides an objective criterion. The repealed instrument is identified in Schedule 2 by a descriptive title rather than a formal instrument name or registration number. The instrument is made by the Chief Metrologist alone, not by the Minister or the National Measurement Institute board. That reflects the delegation of power under paragraphs 8A(1)(a) and (b) of the Act.

The determination directly applies to the Chief Metrologist and the National Measurement Institute as the authority responsible for maintaining Australia's legal measurement standards. It affects any person or entity that is required by law to use a recognised-value standard of measurement when measuring or certifying the density of water. This includes entities such as National Association of Testing Authorities (NATA) accredited laboratories that perform density calibrations for trade, legal metrology officers who verify instruments used for measuring the volume or mass of liquids, and manufacturers of hydrometers, density meters, and related instruments that must be verified for trade use under the National Measurement Act 1960 and associated regulations. The determination also affects parties to commercial transactions where the density of water is used to convert between mass and volume, for example in the sale of bulk liquids, beverages, chemicals, or petroleum products. When a dispute arises about the density of water used in such a conversion, the determination provides the legal reference value that a court or tribunal will apply. The determination therefore indirectly affects all businesses that trade in liquids where volume and mass figures must be reconciled. It also affects government agencies such as state and territory weights and measures authorities, the Australian Competition and Consumer Commission in its administration of trade measurement law, and the National Measurement Institute itself when it issues certificates of verification or calibration. Scientific and research organisations that conduct measurements for regulatory compliance may also find this determination relevant. However, the determination does not impose any direct obligations on consumers, small businesses, or the general public. It does not require any person to take any action, obtain any approval, or pay any fee. Its effect is to provide a legal reference point. Anyone who needs to prove or contest the density of water for legal purposes will rely on this instrument. The determination does not apply to activities that are purely scientific, where no legal or trade purpose is served. It also does not apply to measurements taken outside the temperature range of 0 °C to 40 °C or outside the pressure range of 2 × 10⁴ Pa to 10⁶ Pa, because the standard is not defined for those conditions. Persons or entities measuring water density outside those ranges must use some other reference, which will not have the legal status of a recognised-value standard under the National Measurement Act. The instrument also affects the Chief Metrologist and staff of the National Measurement Institute who must maintain consistency with this standard when performing their functions under the Act. The repeal of the previous determination by Schedule 2 means that any previous calibration or verification certificate that referred to the old standard may need to be reassessed if it remains legally operative. Affected parties should check whether their instruments were certified against the old standard and whether recertification is required.

The determination does not impose duties directly on private persons. Instead, it confers a legal status on a particular numerical value for water density, and through that status creates rights and obligations indirectly. The key right is the right to rely on the values in the determination as the legal standard for water density in any proceeding or transaction governed by Australian law. A party who measures water density in accordance with the instrument has a defence against a claim that the measurement was inaccurate or not in accordance with law, provided the measurement satisfies the conditions in clause 6(1)(d) regarding temperature uncertainty, pressure uncertainty, and impurity levels. The corresponding duty falls on legal metrology officers and other authorised persons who must apply this standard when verifying or certifying instruments that depend on water density. They are duty-bound to use the values and methods set out in the instrument and not some other reference. The instrument also imposes a duty on any person who purports to use the recognised-value standard to do so correctly, including by performing linear interpolation when the temperature is between two table values, and by applying the pressure correction when the pressure is not 101,325 Pa. A person who misapplies the formula or table could be held to have used an incorrect standard, which may affect the enforceability of contracts, the validity of trade measurements, or the outcome of a dispute. The Chief Metrologist has the right to make or vary this determination, but the determination itself does not create any new rights for the Chief Metrologist. The instrument preserves the right of any person to measure water density by any other method, but such a measurement will not have the status of a recognised-value standard. That means it will not be the legally binding reference in trade or legal proceedings unless the parties otherwise agree. The determination does not create a duty to calibrate or recertify existing instruments. It also does not create a duty to update any existing contractual specifications that refer to water density. However, if a contract or regulation incorporates the legal standard by reference, the new values in this determination may become binding on the parties. The tolerance and uncertainty statement in clause 6(1)(d) does not impose a duty to maintain temperature or pressure within the stated limits. It is a statement about the reliability of the standard, not a compliance threshold. A person may still use the standard outside those limits but cannot rely on the 99 per cent confidence statement. The instrument does not grant any exemptions, waivers, or individual permissions. It applies uniformly to all persons and entities in Australia who need a legal standard for water density. There is no provision for the Chief Metrologist to approve alternative methods for individual users. The determination is a legislative instrument and has the force of law once registered, subject to disallowance by either House of the Commonwealth Parliament.

This determination contains no penalty provisions. It does not create any offences, set any fines, or establish any enforcement powers. Enforcement of measurement standards generally occurs through the National Measurement Act 1960 and the National Trade Measurement Regulations 2009, which contain penalties for using unverified instruments, making false or misleading statements about measurements, or tampering with measurement equipment. This instrument merely provides the technical reference against which such enforcement actions can be judged. For example, if a trader is prosecuted for selling a quantity of liquid that is less than the stated amount, the density of water may be relevant to converting a volume measurement into a mass measurement. The court would refer to this determination to determine the legally correct conversion factor. The practical enforcement effect of the determination is therefore indirect. It defines what the law considers to be the correct density value, so a party who uses a different value may be found to have made an inaccurate measurement. The instrument itself carries no criminal or civil penalty for non-compliance because it does not command any conduct. However, using a density value that does not accord with this determination where the law requires use of a recognised-value standard may lead to penalties under the parent Act. The uncertainty statement in clause 6(1)(d) could be relevant in enforcement proceedings. If a measurement challenges the stated confidence bound, a court or enforcement body may need to determine whether the measurement complies with the legal standard. The instrument does not specify how such a determination should be made. The repeal of the previous determination by Schedule 2 means that any enforcement action relying on the old standard after the commencement of this instrument would be legally unsound. The new determination becomes the sole legal reference. There is no provision for transitional enforcement or grace periods. The instrument has no stated penalty for using an incorrect interpolation method or for failing to apply the pressure correction. Those failures would simply mean the measurement does not satisfy the legal standard, leaving the party vulnerable to challenge on the accuracy of their measurement. The National Measurement Institute may take administrative action, such as withdrawing accreditation or cancelling a certificate of verification, for failures to use the correct standard. Those actions are taken under the National Measurement Act and the Institute's own policies, not under this determination. The determination does not create any private right of action. A person who suffers loss because another used an incorrect density value may have a claim for breach of contract, misrepresentation, or misleading conduct, but that claim arises under other law, not this instrument. The determination is purely definitional.

This determination is made under paragraphs 8A(1)(a) and (b) of the National Measurement Act 1960. Those paragraphs empower the Chief Metrologist to determine recognised-value standards of measurement for physical quantities. The determination therefore sits within the hierarchy of Australia's national measurement legislation. The parent Act provides the framework for legal units of measurement, trade measurement, verification of instruments, and enforcement. This instrument fills in the technical detail for one specific quantity. The determination interacts with the National Trade Measurement Regulations 2009 and any state or territory trade measurement legislation that adopts the Commonwealth standards. When those regulations require a measurement to be based on a recognised-value standard, this determination supplies the specific numerical values. The instrument also interacts with Australian standards and codes that reference water density for compliance purposes. For example, standards for hydrometers, density meters, and volume measuring instruments issued by Standards Australia or adopted by regulators may incorporate this determination by reference. The determination does not override or repeal any provision of the parent Act or any other Act. It is subordinate legislation. If there were any inconsistency between this instrument and the National Measurement Act 1960, the Act would prevail. No such inconsistency is apparent. The determination interacts with the general law of contract and tort indirectly. When parties to a contract agree on a quantity that depends on water density, the court will look to the legal standard to determine the correct figure in the absence of contrary agreement. The determination may therefore affect the interpretation of contracts that use terms such as standard density, density of water, or specific gravity without defining the reference. The instrument does not interact with international law or international standards directly. The density values are based on a specific formula that is not identical to any particular international standard, though it is consistent with the known physical properties of water. The determination does not incorporate any external documents by reference. All necessary information is contained within the instrument itself. The determination repeals the previous standard for density of water, so it supersedes that earlier instrument entirely. Any other legislative instrument that referred to the previous standard may need amendment, but that is not addressed in this instrument. The determination does not affect any other recognised-value standards for other physical quantities, such as the standard for density of air, standard for viscosity, or standard for length. Each such standard is the subject of a separate determination. The instrument does not affect any state or territory laws except to the extent that those laws rely on the national measurement framework. If a state law provided for its own water density standard, that provision would be inconsistent with the Commonwealth framework and likely invalid under section 109 of the Constitution, though the instrument itself does not address this. The determination does not create any interaction with taxation law, corporations law, environmental law, or workplace health and safety law, except indirectly through the measurement of quantities subject to those laws.

The determination itself is a new instrument made on 9 March 2026 and signed by Dr Victoria Anne Coleman as Chief Metrologist. It has no amendment history because it has not been amended since its making. The instrument will not be amended after its registration unless the Chief Metrologist issues a further determination under section 8A of the National Measurement Act 1960 that amends or replaces it. The instrument's commencement provision states that it takes effect the day after registration. There are no transitional provisions, savings provisions, or application provisions. The instrument does not contain any clauses anticipating future amendments. The only amendment-related content is in Schedule 2, which repeals the earlier determination. The earlier instrument is described in Schedule 2 as the National Measurement Act 1960 Determination by the National Standards Commission Recognized-Value Standard of Measurement of Density Water. No registration number or date is given for the repealed instrument. The repeal is complete; the whole of the earlier instrument is repealed. There is no grandfathering of certifications, verifications, or measurements made under the old standard. Practitioners should assume that the old standard ceases to have legal effect from the commencement of this instrument. The instrument does not state whether it is a replacement of or a variation to any previous standard, but the repeal of the earlier instrument suggests it is a full replacement. There is no indication in the instrument of which prior instrument it replaces, its date, or its registration details. Practitioners may need to locate the prior instrument separately to understand the full history of the standard. The instrument does not contain a note explaining the reason for the new determination. It does not reference any review, consultation, or scientific update that prompted the change. The explanatory statement, if any, would be a separate document. The instrument does not indicate whether the density values have changed from the previous standard or whether only the legal form has been updated. Without the previous instrument, it is impossible to determine from this source alone whether the numerical values are different. The instrument does not include any transitional arrangements for instruments, certificates, or approvals that referenced the previous standard. There is no provision stating that existing references to the old standard are to be read as references to the new standard. That gap may create legal uncertainty for instruments that were verified or calibrated under the old standard and remain in service.

The source text of this determination does not mention any litigation history. The instrument is newly made as of 9 March 2026 and has not been the subject of any court proceedings. The previous determination that it repeals may have been considered in litigation under the National Measurement Act 1960, but this instrument does not reference any such cases. There is no case law cited in the determination, no preamble referencing legal disputes, and no savings provision preserving the effect of any judicial interpretation of the prior standard. The determination itself sets out technical numerical values and formulas that are unlikely to be the direct subject of litigation. Any disputes would more likely concern the application of these values in trade measurement proceedings, prosecutions for short measure, or civil claims for inaccurate measurement. In such proceedings, the court would take judicial notice of this legislative instrument and apply its values. The legal question would be whether the party correctly applied the standard, not whether the standard itself is valid. The instrument has not been challenged on constitutional grounds, as a determination under section 8A of the Act is a routine exercise of delegated power. No litigation has considered the specific formula, the interpolation method, or the uncertainty statement. The instrument does not preserve any common law or equitable principles relating to measurement. It is a pure legislative instrument. The lack of litigation history may also reflect the specialised and technical nature of the subject matter. Density of water is a settled physical quantity, and disputes are more likely to concern the accuracy of particular instruments or the conduct of particular parties rather than the legal standard itself. If there has been any previous litigation concerning the recognised-value standard for density of water, it is not recorded in this instrument. Practitioners researching the legal history of density standards in Australia should consult court databases and the National Measurement Institute separately. The determination is too recent to have generated any judicial consideration. Any future litigation will depend on how the determination is applied in practice and whether any party challenges the correctness of the values or the method of calculation. Given the probabilistic nature of the uncertainty statement, there may be scope for argument about whether a particular measurement falls within the expected tolerance. No precedent exists under this instrument to guide such arguments.

Several features of this determination may catch out practitioners who do not read the instrument closely. First, the density values in Schedule 1 are given at standard atmospheric pressure of 101,325 Pa only. Many users will measure water density at or near that pressure, but anyone who assumes the table values apply at any pressure will be wrong. The pressure correction in clause 6(1)(c) is mandatory when p differs from 101,325 Pa, even by a small amount. The correction uses a quadratic expression in temperature multiplied by 10 to the power of negative 7 and by the pressure difference. For small pressure differences the correction is small, but for pressures near 10⁶ Pa it can be significant. Second, the linear interpolation method in clause 6(1)(b) is mandatory for intermediate temperatures at standard pressure. A user who applies the formula directly for any intermediate temperature rather than interpolating from the table is not using the legal standard. The formula is provided for information but the legal values are the table values and the interpolated values derived from them. This point could be easily missed. Third, the uncertainty statement in clause 6(1)(d) imposes conditions that may not be met in routine practice. The temperature tolerance is plus or minus 0.1 °C, the pressure tolerance is plus or minus 1,000 Pa, and the impurity tolerance is 1 part in 10⁵ by mass. A practitioner who does not verify these conditions before using the standard cannot rely on the 99 per cent confidence interval. The measurement may still be valid as a legal standard, but the uncertainty is not guaranteed. Fourth, the determination applies only within the stated temperature range of 0 °C to 40 °C and pressure range of 2 × 10⁴ Pa to 10⁶ Pa. Outside those ranges, the instrument provides no recognised-value standard. A person measuring density outside those ranges cannot rely on this instrument at all. Fifth, the repeal of the previous determination in Schedule 2 is complete and has no transitional provisions. Instruments verified or calibrated under the old standard may no longer be legally valid if they depend on the density standard. There is no grandfathering clause. Sixth, the determination does not define the term quality of water for purposes of the impurity limit. It specifies parts per 10⁵ by mass but does not specify which impurities count or how they are measured. This could lead to disputes about compliance with the condition. Seventh, the determination does not specify the required uncertainty in the measurement of temperature or pressure. It only requires that the value used does not differ from the true value by more than the stated amount. A practitioner must have independent knowledge of the true mean temperature and true mean pressure, which may require calibrated instruments whose own calibrations rely on recognised-value standards. Eighth, the instrument does not state whether the standard applies to any type of water or only to pure water. The impurity limit provides some guidance but does not address dissolved gases. Ninth, the determination does not provide a formula for density above 40 °C or below 0 °C. Anyone measuring hot water or ice water solutions has no recognised-value standard under this instrument. Tenth, the instrument is a legislative instrument subject to disallowance by Parliament. A practitioner who relies on it should check that it has not been disallowed before commencing proceedings or completing transactions.

Compliance with this determination is not a matter of taking any positive action but of correctly using its values when the law requires a recognised-value standard for the density of water. The steps are as follows. First, determine the temperature of the water in degrees Celsius and the mean pressure in pascals. The temperature must be within 0 °C to 40 °C and the pressure within 2 × 10⁴ Pa to 10⁶ Pa for the standard to apply. Second, at standard atmospheric pressure of 101,325 Pa, look up the temperature in Schedule 1. If the temperature is exactly one of the listed values, use the corresponding density from the table. If the temperature is between two listed values, perform linear interpolation between the two nearest entries. For example, at 10.05 °C, the density is halfway between the value at 10.0 °C (999.700 kg·m⁻³) and the value at 10.1 °C (999.691 kg·m⁻³), giving 999.6955 kg·m⁻³. The instrument does not specify rounding rules for the interpolated value, but common practice would be to report to the same number of decimal places as the table. Third, if the pressure is not 101,325 Pa, apply the pressure correction formula. The correction is: (5.0619 − 0.0309 × t + 0.0003614 × t²) × 10⁻⁷ × (p − 101325). The correction is added algebraically to the density obtained from the table or interpolation. For example, at 20 °C and 200,000 Pa, the correction would be (5.0619 − 0.0309 × 20 + 0.0003614 × 400) × 10⁻⁷ × (200,000 − 101,325). That equals (5.0619 − 0.618 + 0.14456) × 10⁻⁷ × 98,675 = 4.58846 × 10⁻⁷ × 98,675 = 0.0453 kg·m⁻³ approximately. So the corrected density at 20 °C and 200,000 Pa is 998.204 + 0.0453 = 998.249 kg·m⁻³. Fourth, if the result is to be relied upon with the 99 per cent confidence statement, the practitioner must ensure that the temperature used does not differ from the true mean temperature by more than 0.1 °C, the pressure used does not differ from the true mean pressure by more than 1,000 Pa, and impurities in the water do not exceed 1 part in 10⁵ by mass. This may require calibration of thermometers and pressure gauges and chemical analysis of the water. Fifth, for legal proceedings or trade transactions, keep records of the temperature, pressure, impurity level, and the source of the density value (table, interpolation, or corrected). This will allow verification that the standard was correctly applied. Sixth, if an instrument was certified or verified under the previous standard, check whether recertification is needed. The repeal in Schedule 2 does not explicitly address this, so legal advice may be prudent. Seventh, if the measurement involves water density for a purpose other than trade or legal compliance, the instrument may not apply. Compliance is only required where the law mandates use of a recognised-value standard.