A US half barrel — the keg most people mean when they say "a keg" — holds 165 twelve-ounce beers or 124 pints. But you will never pour that many, and the gap matters when you are deciding how much to buy.
Where the sizes come from
One number defines everything: a US beer barrel is exactly 31 US gallons, set in federal regulation. Every keg is a fraction of it. A half barrel is 15.5 gallons, a quarter is 7.75, a sixth is 5.17. That is why keg volumes look like such odd numbers.
Every keg size
| Keg | Litres | 12 oz beers | 16 oz pints |
|---|---|---|---|
| Half barrel (US standard) | 58.67 | 165 | 124 |
| Quarter barrel (pony keg) | 29.34 | 82 | 62 |
| Sixth barrel (sixtel) | 19.55 | 55 | 41 |
| Cornelius (corny keg) | 18.93 | 53 | 40 |
| 50 L import / European | 50 | 140 | 105 |
| Mini keg (bubba) | 5 | 14 | 10 |
UK and Australian pours
Both markets are metric and both use 50 L as the standard. The serving sizes differ, so the yields do too.
| Keg | UK pints (568 ml) | Schooners (425 ml) | Pots (285 ml) |
|---|---|---|---|
| 50 L | 88 | 118 | 175 |
| 30 L | 52 | 70 | 105 |
| 20 L | 35 | 47 | 70 |
| Firkin (40.9 L) | 72 | 96 | 143 |
The foam problem — and a number to distrust
Those figures are nominal. Real kegs lose beer to foam, to priming the lines, and to the sediment at the end. A well-tuned home system loses about 5%. A professional bar with short, cold lines gets to 3%. Long lines on a warm day can reach 10%.
So plan on a half barrel pouring 110–118 pints, not 124.
Now the number to be careful with. You will see it stated that foam is 25–30% beer, and you will see sites treat that as a loss rate — concluding a half barrel yields only about 90 pints. That is wrong. The 25–30% figure describes what foam is made of, not what share of your keg disappears into it. Two completely different measurements.
How many kegs for your party
Use the caterer's formula — two drinks in the first hour, one per hour after, or guests × (hours + 1) — then take the share who actually drink beer.
| Party | Total drinks | Beers (40% share) | Half barrels |
|---|---|---|---|
| 50 guests, 4 hours | 250 | 100 | 1 |
| 100 guests, 4 hours | 500 | 200 | 2 |
| 100 guests, beer-only | 500 | 500 | 4 |
| 150 guests, 5 hours | 900 | 360 | 3 |
The "share who drink beer" is the variable people forget. At a wedding with wine and a cocktail bar, beer might be a quarter of drinks. At a backyard barbecue it might be everything.
Is a keg actually cheaper?
At scale, usually. A half barrel holds roughly what seven cases of 24 hold, and per serving it typically lands around 55–65% of the cost of cans. The break-even is somewhere near a 30-guest party — below that, the deposit, the tap rental and the leftover beer wipe out the saving.
Be sceptical of specific dollar figures you find online, including in the sources that publish them: keg pricing swings hard by state and distributor, and readers frequently report their local numbers look nothing like the quoted ones. Trust the ratio, not the price tag.
Practical things people forget
- Ice. A half barrel needs roughly 18 kg (40 lb) of ice in a tub to hold temperature through a party.
- Chill it overnight. A warm keg foams catastrophically and you will pour half of it onto the grass.
- Cups. Plan 1.5 per beer-drinking guest.
- Weight. A full half barrel is about 160 lb (72 kg). That is a two-person lift, and it will not go up stairs easily.
The keg calculator converts any keg size into any serving size and works out how many you need for your guest count and beer share.