How much beer is in a keg?
Keg sizes in the United States are fractions of a 31-gallon barrel. One US fluid ounce is 29.57 mL, so a keg’s volume converts directly into servings.
| Keg | Volume | 12 oz servings | 16 oz pints |
|---|---|---|---|
| Half barrel (full-size) | 15.5 gal (1,984 oz) | 165 | 124 |
| Quarter barrel (pony) | 7.75 gal (992 oz) | 82 | 62 |
| Sixth barrel | 5.16 gal (661 oz) | 55 | 41 |
| Cornelius keg | 5 gal (640 oz) | 53 | 40 |
| 50 liter European keg | 13.2 gal (1,691 oz) | 140 | 105 |
These are theoretical maximums. Foam, the first pours and the beer left at the bottom typically waste 5 to 10%, more if the keg is warm or shaken.
The formula
Glasses per keg = keg volume ÷ glass size × (1 − loss)
Kegs needed = guests × beers per guest ÷ glasses per keg, rounded up.
Example
A half barrel served in 12 oz cups with 5% loss gives 1,984 ÷ 12 × 0.95 = 157 cups. For 80 guests drinking 3 beers each (240 cups), you need 2 kegs. At $150 a keg, each cup costs about $0.96, against $1.50 to $2 for cans.
How many beers per guest?
A common rule is one drink per guest per hour, plus one extra in the first hour. Adjust for your crowd, the time of day and whether wine or cocktails are also served.
Tips for a good pour
- Keep the keg at 36 to 38 °F; warm beer foams.
- Let a transported keg rest for a few hours before tapping.
- With a party pump, pump only when the flow slows: over-pumping adds air and makes the beer go flat within a day.
- A CO2 tap system keeps a keg fresh for weeks; a hand pump keeps it for about 24 hours.
Check local rules: many retailers require a deposit for the keg and tap, and some places require keg registration.
Serve responsibly and arrange safe rides home for guests.