Alcohol Units and Standard Drinks Calculator

This calculator is designed to convert a measured volume of whisky and its labelled alcohol strength into units or standard drinks for a selected country. It calculates the alcohol in that serving, not an allowance to drink or a prediction about driving.

[TOOL TO BUILD]

How to use the calculator

Enter the serving volume in millilitres, then enter the alcohol by volume shown on the label as a percentage. Choose the country whose unit or standard drink definition you want to use, and check all three inputs before calculating.

Use the quantity actually measured, rather than a glass size or a guessed pour. If the serving contains more than one alcoholic ingredient, enter each ingredient separately with its own volume and strength; the calculator should show their combined result.

What the result will show

The result should display the entered serving size, labelled strength, selected country and calculated amount. It should name the measure explicitly, rather than showing an unexplained number: a result labelled only “drinks” is not clear enough.

Changing the country must change the reference definition, not the amount of liquid entered. The selected definition, its source and its verification date should remain visible beside the result so that the calculation can be understood on its own.

Calculation method

The first step calculates the volume of pure alcohol from the two numerical inputs. For a definition expressed by mass, convert that volume to mass using a documented density factor before dividing by the selected reference quantity.

Pure alcohol (ml) = serving volume (ml) × ABV (%) ÷ 100

If a national definition expresses alcohol by mass rather than volume, the conversion also needs a documented density factor. The tool must not treat grams and millilitres as interchangeable or apply a country conversion without its supporting reference.

Inputs and limits

Missing values should produce a request to complete the relevant field, not a zero result. Negative volumes and strength values outside zero to one hundred per cent should be rejected; an unsupported country definition should display “not verified”, not an estimated conversion.

Results should be rounded only for display, with the rounding rule explained beside them. Keep the original inputs visible so that a misplaced decimal point or an incorrect serving size can be corrected without starting again.

What this calculator cannot tell you

This is a quantity calculator, not a personal health assessment. It must not label a result safe, recommend another serving, estimate when someone can drive, or turn a calculation into a drinking target.

Sources

The master prompt supplies definitions for UK units and US and Australian standard drinks. Their authoritative sources and the density factor needed for mass conversions must be checked and documented before the calculator is activated.

This draft was prepared from the supplied item brief as a calculator specification, without adding country conversion constants or drinking guidance.

Last checked: November 2026