The unit calculation is simple once you know the formula. The hard part is knowing the volume and ABV of what you’re drinking, because pubs and restaurants don’t usually display the ABV next to your drink. This article gives you the formula, worked examples for every common drink type, and the mental shortcuts for estimating without a calculator. This article is part of our Alcohol Units hub, the complete guide to alcohol unit measurement.
This article covers the UK unit formula primarily, with conversions to US standard drinks and Australian standard drinks at the end. The math is identical; only the round-number multiplier changes.
# The basic formula
For UK alcohol units, the formula is:
Units = (volume in ml × ABV) ÷ 1000
Where ABV is the percentage as a whole number (so 5% becomes 5, not 0.05).
For example, a 568ml pint of 5% lager:
- (568 × 5) ÷ 1000 = 2.84 units
A 175ml glass of 12.5% wine:
- (175 × 12.5) ÷ 1000 = 2.19 units
A 50ml home measure of 40% spirit:
- (50 × 40) ÷ 1000 = 2 units
The formula works for any drink. Volume in millilitres, ABV as a percentage, divide by 1000.
# Worked examples for common drinks
# Beer
A standard UK pint is 568ml. The strength varies dramatically:
- Pint of 3.5% mild bitter: (568 × 3.5) ÷ 1000 = 2 units
- Pint of 4% standard lager (Carling, Foster’s): (568 × 4) ÷ 1000 = 2.27 units
- Pint of 5% premium lager (Heineken, Stella): (568 × 5) ÷ 1000 = 2.84 units
- Pint of 5.5% IPA: (568 × 5.5) ÷ 1000 = 3.12 units
- Pint of 6% pale ale: (568 × 6) ÷ 1000 = 3.41 units
- Pint of 7.5% IPA (BrewDog Hazy Jane): (568 × 7.5) ÷ 1000 = 4.26 units
- Pint of 9% imperial stout: (568 × 9) ÷ 1000 = 5.11 units
Three pints of 5.5% IPA: 9.36 units in one session. That’s two-thirds of the UK weekly guideline.
# Bottled and canned beer
Bottle and can sizes vary:
- 330ml bottle of 5% lager: (330 × 5) ÷ 1000 = 1.65 units
- 440ml can of 5% lager: (440 × 5) ÷ 1000 = 2.2 units
- 500ml can of 6% IPA: (500 × 6) ÷ 1000 = 3 units
- 660ml bottle of 4.5% beer: (660 × 4.5) ÷ 1000 = 2.97 units
- 750ml bottle of 6% beer (sharing format): (750 × 6) ÷ 1000 = 4.5 units
A 4-pack of 440ml cans at 5%: 8.8 units total.
# Wine
Glass sizes vary by venue and home pour:
- Small 125ml of 12% wine: (125 × 12) ÷ 1000 = 1.5 units
- Standard 175ml of 13% wine: (175 × 13) ÷ 1000 = 2.28 units
- Large 250ml of 14% wine: (250 × 14) ÷ 1000 = 3.5 units
- Half bottle (375ml) of 12% wine: (375 × 12) ÷ 1000 = 4.5 units
- Bottle (750ml) of 13% wine: (750 × 13) ÷ 1000 = 9.75 units
- Bottle (750ml) of 14.5% strong red: (750 × 14.5) ÷ 1000 = 10.88 units
A bottle of red wine shared between two people: roughly 5 units each. That’s a third of the weekly guideline in one evening.
# Spirits
The standard UK pub measure is 25ml; some venues serve 35ml:
- 25ml single shot of 40% vodka: (25 × 40) ÷ 1000 = 1 unit
- 35ml shot of 40% gin: (35 × 40) ÷ 1000 = 1.4 units
- 50ml double of 40% rum: (50 × 40) ÷ 1000 = 2 units
- 25ml of 50% spirit (overproof rum, strong gin): (25 × 50) ÷ 1000 = 1.25 units
- 50ml home pour of 40% whisky: (50 × 40) ÷ 1000 = 2 units
- 80ml generous home pour of 40% spirit: (80 × 40) ÷ 1000 = 3.2 units
Most “doubles” at home are 60-80ml, not 50ml. A “couple of whiskies” at home is often 5-6 units, not 2.
# Cocktails
Cocktail unit content depends on what’s in them. Approximate units for common cocktails (single serving):
- Gin and tonic (35ml gin, 40% ABV): 1.4 units
- Vodka soda (35ml vodka, 40%): 1.4 units
- Margarita (50ml tequila + 25ml triple sec): 2.5 units
- Mojito (50ml rum, 40%): 2 units
- Old Fashioned (60ml whiskey, 40%): 2.4 units
- Negroni (30ml gin + 30ml Campari + 30ml vermouth): 2.5 units
- Espresso martini (50ml vodka + 25ml coffee liqueur): 2.5 units
- Long Island iced tea (15ml each of 5 spirits at 40%): 3 units
- Piña colada (50ml rum, sometimes more): 2-3 units
Strong craft cocktails at home or in cocktail bars can run higher. A double Old Fashioned with 100ml of bourbon is 4 units.
# Cider
Cider strength varies more than people expect:
- Pint (568ml) of 4.5% standard cider: (568 × 4.5) ÷ 1000 = 2.56 units
- Pint of 5% cider (Strongbow Original): (568 × 5) ÷ 1000 = 2.84 units
- Pint of 6% premium cider: (568 × 6) ÷ 1000 = 3.41 units
- 500ml bottle of 7% strong cider: (500 × 7) ÷ 1000 = 3.5 units
- 2-litre bottle of 7.5% white cider: (2000 × 7.5) ÷ 1000 = 15 units
A 2-litre bottle of strong white cider is the entire UK weekly guideline in one container.
# Hard seltzers and ready-to-drink
These tend to be lower in alcohol per serve but often consumed in volume:
- 330ml can of 4% hard seltzer: (330 × 4) ÷ 1000 = 1.32 units
- 330ml can of 5% White Claw: (330 × 5) ÷ 1000 = 1.65 units
- 250ml can of 6% RTD cocktail: (250 × 6) ÷ 1000 = 1.5 units
- 275ml bottle of 4% alcopop: (275 × 4) ÷ 1000 = 1.1 units
A 4-pack of hard seltzer is roughly 6.6 units, similar to two pints of standard lager.
# The mental shortcut: rough estimates without a calculator
For quick estimation without doing precise arithmetic:
# The “1 unit per pint percent” shortcut
A UK pint of 1% beer would be 0.568 units. Round that to 0.6, and you get a useful rule:
Units in a pint ≈ ABV × 0.6 (slightly low, but easy)
Or more precisely:
Units in a pint ≈ ABV × 0.57
So:
- Pint of 4% beer: 4 × 0.6 = 2.4 (actual: 2.27)
- Pint of 5% beer: 5 × 0.6 = 3 (actual: 2.84)
- Pint of 6% beer: 6 × 0.6 = 3.6 (actual: 3.41)
- Pint of 8% beer: 8 × 0.6 = 4.8 (actual: 4.54)
Not perfect but close enough for in-the-moment estimation.
# The “wine glass anchor”
A standard 175ml UK glass at 13% (typical for most table wine) is roughly 2.3 units. From that anchor:
- Smaller 125ml glass: 1.6 units
- Larger 250ml glass: 3.3 units
- Whole bottle (750ml): 9.75 units
Strong wines (14-15%) add about 8% to those numbers; light wines (10-11%) reduce by about 12%.
# The “spirit shot anchor”
A 25ml UK pub measure of 40% spirit is exactly 1 unit. From that:
- 35ml measure: 1.4 units
- 50ml double: 2 units
- 50ml home pour: 2 units (most home pours)
- 70-80ml generous home pour: 3 units
# The “session estimator”
Add up the rough unit count for typical sessions:
- 4 pints of standard lager: 9-11 units
- 6 pints of standard lager: 14-17 units (over the weekly guideline)
- Bottle of wine to yourself: 9-10 units
- 2 cocktails plus a couple of glasses of wine: 7-9 units
- 4 spirits at the pub: 4 units
- 4 spirits at home (typical pours): 8 units
# When the math is harder
A few situations where calculation requires more care:
# Variable ABV products
Some craft beer and spirits don’t display ABV prominently on the menu. Ask, or assume the high end of the typical range for the style.
# Cocktail variations
Cocktails made at home or by amateur bartenders vary widely. A “margarita” at one bar might have 30ml of tequila; another might have 60ml. When unsure, assume the higher end.
# “Strong” or “double” drinks
When you order or pour something described as “strong,” ask what that means in volume terms. “Strong gin and tonic” can mean 50ml, 70ml, or “I just kept pouring.”
# Mixed drinks at parties
The “punch” or pre-mixed cocktail at parties is the most uncertain. Sweet flavours mask alcohol; volume is hard to gauge from a cup. Assume 1.5-2 units per cup of punch as a baseline.
# Imperial vs metric measures
US bottles and recipes use ounces. To convert to metric: multiply ounces by 30 to get approximate millilitres (more precisely, 29.57). A 12oz beer is 355ml; a 1.5oz shot is 44ml.
# Conversions to other systems
The calculation gets you UK units. To convert to other systems:
# To US standard drinks
US standard drink = 14g of alcohol = 17.7ml of pure alcohol.
US drinks = UK units × 0.57
So 14 UK units = 8 US standard drinks.
# To Australian standard drinks
Australian standard drink = 10g of alcohol = 12.5ml of pure alcohol.
Australian drinks = UK units × 0.8
So 14 UK units = 11.2 Australian standard drinks.
# To grams of pure alcohol
Grams = UK units × 8
So 14 UK units = 112g of alcohol per week.
# Practical applications
A few places this calculation matters:
# Comparing to local guidelines
The first practical use: knowing whether your drinking is within or outside your local low-risk guidelines.
UK: 14 units per week max. US: 14 standard drinks (men) or 7 (women) per week max. Australia: 10 standard drinks per week max.
These look superficially similar but represent different actual alcohol amounts as covered in the pillar.
# Choosing drinks during a session
Once you know the unit math, you can make informed choices during a session. If you’ve planned for 6 units, a pint of 4% beer (2.3 units) leaves room for a 250ml glass of wine. A pint of 7% IPA (4 units) doesn’t.
# Tracking progress
If you’re trying to drink less, the unit count gives you a clear measurement. “Drink fewer pints” is vague. “Stay below 10 units a week” is actionable.
# Driving decisions
In the UK, the legal driving limit corresponds roughly to 1 unit for most adults under most conditions. But the actual blood alcohol depends on your weight, sex, food in stomach, and time elapsed. The unit count is a starting point, not a permission to drive.
# How AlcoLog handles unit calculation
AlcoLog calculates units automatically. The catalogue includes 273 drinks at 87 size presets, all with accurate ABV and volume. When you log a drink, the app pulls the correct unit value from the catalogue.
For drinks not in the catalogue, the Add Drink screen lets you specify volume and ABV manually. The app calculates units automatically once you enter those two values.
The session-end summary shows total units alongside drinks, calories, and cost. Over time, the History view aggregates units by week and month for comparison against your guidelines.
If you travel and want to see your data in a different unit system, the locale-aware display switches automatically based on device settings.
