Punch calculator · alcohol strength
Punch calculator – work out the alcohol strength of a drink
Add each ingredient with its amount and strength, and the calculator gives the final alcohol strength of the mix, the total volume in litres, the amount of pure alcohol and the servings per guest. It works just as well for a single drink as for a hundred-litre punch bowl.
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How the strength of a mix is worked out
A common mistake is to average the ingredients' percentages. That gives the wrong answer, because the percentages aren't equally weighted – a seven-decilitre bottle of vodka affects the result completely differently from a ten-millilitre dash of liqueur. The right way is to weight each strength by its volume.
strength = Σ(amount × strength) / total volume
Example: 700 ml of vodka (40%), 2,000 ml of juice (0%) and 750 ml of sparkling wine (11%).
The pure alcohol comes to 700 × 0.40 + 750 × 0.11 = 280 + 82.5 = 362.5 ml.
The total volume is 3,450 ml, so the strength is 362.5 / 3,450 × 100 = 10.51% ABV.
Ice and water belong in the calculation, because they add to the total volume and dilute the drink. Melting ice dilutes the punch further during serving, so the strength of the finished drink falls by a few tenths over the evening.
How much punch you need – quantities for a party
Estimating the total is as important as the strength. As a practical rule of thumb, punch goes at about two
servings per guest in the first hour and roughly one serving an hour after that. At 200 ml a serving, a three-hour
party for twenty guests needs about
20 × 4 × 200 ml = 16 litres.
| Guests | 2 hours | 3 hours | 4 hours |
|---|---|---|---|
| 10 | 6 l | 8 l | 10 l |
| 20 | 12 l | 16 l | 20 l |
| 30 | 18 l | 24 l | 30 l |
| 50 | 30 l | 40 l | 50 l |
The calculator tells you directly how many servings the mix makes and how much is enough for one guest. It's worth providing at least as many alcohol-free options – designated drivers, pregnant guests and under-18s are at almost every party.
Strengths of common drinks
| Drink | Strength (% ABV) | Typical pack |
|---|---|---|
| Lager | 4.0–5.5 | 330 ml / 500 ml |
| Cider | 4.5–5.5 | 440 ml |
| Ready-to-drink can | 5.0 | 250 ml |
| White wine | 11–13 | 750 ml |
| Red wine | 12–14.5 | 750 ml |
| Sparkling wine | 11–12 | 750 ml |
| Liqueurs | 15–30 | 500 ml / 700 ml |
| Vodka, gin, rum | 37.5–40 | 700 ml |
| Juice, soft drink, water | 0 | – |
The exact strength is always on the bottle label – use that if you want a precise result. This site is not a retailer and does not sell alcohol.
One UK unit and pure alcohol
In the UK, "one unit" of alcohol is 10 ml (about 8 g) of pure alcohol, which is roughly a single 25 ml measure of spirits, or about a third of a 175 ml glass of wine. The calculator shows the amount of pure alcohol in millilitres, so you can work out how many units are in the punch bowl yourself.
This calculator gives the strength of the drink, not your blood alcohol level. Blood alcohol depends on weight, sex, time, food and individual differences, and cannot be deduced from the percentages of a drink. Don't use the calculator to judge your fitness to drive or how sober you are. If you're looking for a blood-alcohol tool, use dedicated health services – and if you're driving, don't drink.
Diluting and strengthening
If the finished drink is too strong, dilution is worked out with the same formula. A three-litre mix at 14%
contains 420 ml of pure alcohol. When you add a litre of juice, the total is 4 litres and the strength is
420 / 4,000 × 100 = 10.5%. In practice: add the juice or water on its own row at 0% strength and check
the result.
The other way: to raise a 10-litre 8% punch to 12%, you need more spirit. Try different amounts in the calculator – the result updates as you type, so the right amount turns up in a few seconds.
The basics of alcohol-strength calculation
The strength of a mix is a volume-weighted average of the ingredients – not an average of the percentages.
Formulas and examples
Strength of the mix
Σ(amount × strength) / total volumeExample
700 ml/40% + 2,000 ml/0% + 750 ml/11%: 362.5 / 3,450 × 100 = 10.51% ABV.
Note
Averaging the percentages would give 17% – completely wrong.
Amount of pure alcohol
Σ(amount × strength / 100)Example
In the mix above, 362.5 ml of pure alcohol.
Note
One UK unit is 10 ml (about 8 g) of pure alcohol.
Dilution
new strength = alcohol / (old volume + added liquid)Example
3 l of mix at 14% + 1 l juice: 420 / 4,000 × 100 = 10.5%.
Note
Add the liquid on its own row at 0% strength.
Amount per guest
total volume / number of guestsExample
16 l / 20 guests = 800 ml, i.e. four 200 ml servings.
Note
Rule of thumb: 2 servings in the first hour, 1 serving/hour after.
Concepts and classification
| % ABV | Alcohol by volume – the share of alcohol in the drink's volume. |
|---|---|
| Pure alcohol | The amount of ethanol in millilitres. |
| Unit (UK) | 10 ml (about 8 g) of pure alcohol. |
| Diluent | Water, ice, juice or soft drink – 0% strength. |
| Spare allowance | Extra provision for spills and leftovers. |
Limitations of the calculator
- The calculator does not tell you your blood alcohol level or units per hour cleared.
- The result does not tell you when it's safe to drive or to be sober.
- Melting ice dilutes the drink further during serving.
- Alcohol by volume and alcohol by mass cannot be equated.
How up to date the information is
When it was checked
Content and the figures used were checked on 12 August 2026.
Disclaimer
The calculator gives a mathematical result from the numbers you enter. It is not an official decision, an offer or professional advice. See the terms of use.
Topics
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Frequently asked questions about the punch calculator
How do I work out the ABV of a punch?
Multiply each ingredient's volume by its strength, add the results and divide by the total volume: Σ(amount × strength) / total. Don't average the percentages – that gives the wrong answer, because the ingredient amounts differ.
Do ice and water count?
Yes. They increase the total volume and dilute the drink, so add them on their own row at 0% strength. Melting ice dilutes the drink further while it's being served.
How much punch do I need per person?
A rule of thumb is two servings in the first hour and one serving an hour after that. At 200 ml a serving, a three-hour party needs about 800 ml per guest. Enter the number of guests and the serving size for the figures.
Does the calculator tell me my blood alcohol level or whether I can drive?
No, and it cannot. The calculator gives the strength of the drink, not blood alcohol. That depends on weight, sex, drinking time, food and individual differences. Never use the calculator to judge fitness to drive.
How do I dilute a drink that's too strong?
Add an alcohol-free liquid on its own row at 0% strength and see how the strength changes. The result updates instantly, so you can try different amounts and stop at the one that hits your target.