Hong Life CalculatorsUnderstanding the alcohol unit calculator — concept and principle
This calculator adds up the UK alcohol units in up to three kinds of drink a week, then shows the grams of pure alcohol, US standard drinks, the share of the 14-unit low-risk guideline, units per drinking day and units from each drink. People reviewing their drinking and health professionals use it.
How it is calculated
- Units in a drink = volume (mL) × ABV (%) ÷ 1,000
- Weekly units = Σ count × units per drink
- Pure alcohol (g) = units × 8 (one UK unit is 10 mL or 8 g of ethanol)
- US standard drinks = grams ÷ 14
- Share of guideline = units ÷ 14 × 100; units per drinking day = units ÷ days
The principle
Drinks differ widely in size and strength, so counting "drinks" says little. Converting each drink to pure alcohol puts beer, wine and spirits on one scale. A UK unit is 10 mL of ethanol, about 8 g because ethanol's density is about 0.789 g/mL. The UK Chief Medical Officers advise not drinking more than 14 units a week on a regular basis, spread over three or more days, with several drink-free days. A US standard drink is 14 g. There is no completely safe level; lower is lower risk.
Worked example
Defaults: 4 × 500 mL at 5%, 2 × 175 mL at 13%, 1 × 360 mL at 16.5%, drinking on 3 days.
- Drink 1 = 4 × 500 × 5 ÷ 1,000 = 10 units; drink 2 = 2 × 175 × 13 ÷ 1,000 = 4.5; drink 3 = 360 × 16.5 ÷ 1,000 = 5.9.
- Weekly units = 20.5; pure alcohol = 164 g.
- US standard drinks = 164 ÷ 14 = 11.7.
- Share of the 14-unit guide = 146%; units per drinking day = 20.5 ÷ 3 = 6.8.
| Drink 1 (e.g. beer): how many a week | Units per week (UK, 10 mL alcohol) |
|---|---|
| 1 | 13 |
| 2 | 15.5 |
| 3 | 18 |
| 4 | 20.5 |
| 5 | 23 |
| 6 | 25.5 |
| 8 | 30.5 |
How to read the result
This pattern is about 1.5 times the low-risk guideline and concentrated into three days, which raises short-term risks such as injuries. Cutting the largest contributor, here beer, has the biggest effect. If you find it hard to cut down, a doctor or local alcohol service can help.
Common mistakes
- Using a "standard" glass size when your pour is larger.
- Forgetting that ABV varies widely between brands.
- Saving up weekly units for one or two days.
- Mixing UK units with standard drinks from other countries.
Frequently asked questions
How many units are in a pint of beer?
It depends on strength: a 568 mL pint at 4% is about 2.3 units.
How many units are in a bottle of soju?
A 360 mL bottle at 16.5% is about 5.9 units.
Is 14 units a safe limit?
It is a low-risk guideline, not a safe level; drinking less carries less risk.
Sources: UK Chief Medical Officers' Low Risk Drinking Guidelines (Department of Health, August 2016) · NIAAA, "What Is a Standard Drink?"