Discover Harris Organic Alcohol Volume: Great Spirit

Here is a table I use to calculate the alcohol volume of my moonshine or brandies to calculate the exact volume of litres I have from the weight of the spirit in kilogrammes. You can use it too. The data for the conversion is from the International Organisation of Legal Metrology. The International Alcometric Tables. https://www.oiml.org/en/files/pdf_r/r022-e75.pdf

To calculate alcohol volume from weight, Alcohol by Weight (ABW), first find the weight of the alcoholic spirit and divide it by the density of ethanol (approximately 0.789 g/mL or 789 kg/L) to get the volume.

For a more general calculation, you need the product's Alcohol by Volume (ABV) and total volume.
This conversion exists where we multiply the ABV by the density at 20C to get the answer.

NB: Subsection 6(2) of the Distillation Act, subsection 3(2) of the Spirits Act and the preamble to the Schedule to the Excise Tariff Act state, respectively, that the volume of alcohol contained in any liquor or other substance, spirits or goods shall be taken to be the volume that would be the volume of that alcohol if the alcohol were measured at a temperature of 20°C.
Those provisions also specify that the specific gravity of alcohol in relation to water is 0.79067.
All quantities relating to external deliveries and receipts are required to be corrected to 20°C to correctly assess any duty liability in accordance with the Excise Tariff Act.

What’s happening with the different densities?
ATO / Australian law requires you to use a legal specific gravity for pure ethanol at 20 °C of 0.79067 when calculating excise volume. This is prescribed in the Excise Determination and ATO guidance.
OIML and modern metrology use a slightly different, experimentally-derived value (e.g. OIML / international alco-metric tables list ~0.78924). That value comes from up-to-date densitometry and the international alcoholometry literature (European Pharmacopoeia / OIML tables).
Why they differ
Legal vs scientific standards: the ATO figure is a legal constant chosen for consistency and regulatory stability (so excise calculations are reproducible and not shifting when metrology improves). The OIML value is the modern experimental best estimate. Small magnitude: difference ≈ 0.0014 (about 0.18% relative). It’s small, but material for excise money and duty reporting, so law takes precedence for tax purposes.
Where to find the ATO/legal references
Australian Taxation Office practical guidance page: Measuring excisable alcohol volume and strength (states use 0.79067).
The legislative instrument: Excise (Alcoholic Strength of Excisable Goods) Determination 2019 (text confirming the 0.79067 constant).
ATO guidance and excise law also reference using standard practical alcohol tables (AS2371 historically) for hydrometer conversion.
Practical effect for you
For excise returns / compliance: use 0.79067 and follow the ATO/Determination rules (this is legally required).
For production, lab work, R&D or accurate conversion: use OIML / modern density tables (0.78924 and full tables) — they’re more accurate physically.