how many gallons in a firkin

February 23, 2026

A standard beer firkin holds 9 imperial gallons , which is about 10.8 U.S. gallons of liquid.

How Many Gallons in a Firkin?

Quick Scoop

If you’ve heard someone at a pub or in a homebrewing forum ask “how many gallons in a firkin?”, they’re talking about a traditional British cask size used for beer. The key point: a beer firkin is one quarter of a barrel.

1 firkin (beer) = 9 imperial gallons.

That’s approximately 10.8 U.S. gallons.

In litres, that’s about 41 L.

Historically, firkins also appeared as a dry measure in the U.S., defined as 9 U.S. gallons (about 34 L) , but when people say “firkin” today, they almost always mean the beer cask size above.

Mini breakdown: beer nerd edition

Traditional brewery scale (Imperial)
- Tun: 216 imperial gallons
- Butt: 108 imperial gallons
- Hogshead: 54 imperial gallons
- Barrel: 36 imperial gallons
- Kilderkin/Kinderkin: 18 imperial gallons
- Firkin: 9 imperial gallons
- Pin: 4.5 imperial gallons

Modern pub context
- A firkin is a small cask used for cask-conditioned (“real”) ale.

* It’s roughly a quarter of a full barrel and is popular at cask festivals and “firkin Fridays.”

Why the numbers vary online

If you search around, you might see slightly different gallon numbers:

Some sources give about 10.2 U.S. gallons for a firkin.

Others give 10.8 U.S. gallons for the same beer firkin size.

This happens because:

Imperial vs U.S. gallons – an imperial gallon is larger than a U.S. liquid gallon.
Historical redefinitions – older English “ale” and “beer” gallons changed over time, and firkins were redefined along with them.

Modern standardized definition for beer:

1 firkin = 9 imperial gallons = 10.8 U.S. gallons ≈ 41 L.

Quick HTML table (for clarity)

html

<table>
  <thead>
    <tr>
      <th>Measurement</th>
      <th>Beer firkin amount</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Imperial gallons</td>
      <td>9</td>
    </tr>
    <tr>
      <td>U.S. gallons (approx.)</td>
      <td>10.8</td>
    </tr>
    <tr>
      <td>Litres (approx.)</td>
      <td>41</td>
    </tr>
    <tr>
      <td>Fraction of a barrel</td>
      <td>1/4 barrel</td>
    </tr>
  </tbody>
</table>

Forum-style note

On beer and homebrewing forums, when someone asks “how many gallons in a firkin?” the accepted practical answer is:
“Nine imperial, call it about ten and a bit U.S. gallons in the real world.”

TL;DR: For beer, a firkin is 9 imperial gallons , roughly 10.8 U.S. gallons.

Information gathered from public forums or data available on the internet and portrayed here.