Firkin (from Middle Dutch vierdekijn, "fourth", i.e. a quarter of a barrel) may refer to an old English unit of volume or a cask of this volume:
- a beer firkin, 9 imperial gallons (41 litres)
- a wine firkin, 84 wine/US or 70 imperial gallons (318 litres)
Nor need you mind the serial ordeal
Of being watched from forty cellar holes
As if by eye pairs out of forty firkins.
— Robert Frost, "Directive"
Firkin may also refer to:
- an obsolete unit of mass by which butter was sold equal to 56 pounds (25.401 kg)
- an obsolete unit of mass by which soap was sold equal to 64 pounds (29.030 kg)
- a firkin of water (90 lb or 40.823 kg) the base unit of mass in the humorous FFF System
- an antique wooden bucket, usually with wood handle and lid, about 10 inches (250 mm) high and 10 inches in diameter (approximately 790 cu in, 13 l, 2.8 imp gal or 2.9 US dry gal), formerly used to store sugar and other items.
- Firkin (aircraft), an experimental supersonic jet fighter
- Firkin (band), an Irish-punk band
- Firkin Brewery, a chain of pubs in the United Kingdom, and the unrelated "Firkin Group of Pubs" in Canada and the United States
- Firkin Press, a fantasy adventure online magazine published in the United States by Firkin Press
- Firkin Roos, an Australian rules football team in Britain