🏺 History
Historical & Obscure Units Converter
Convert barleycorns, cubits, troy ounces, firkins, hogsheads, roods and hides into modern units — and into each other. Pick a category, enter a value and press Convert.
About the Historical & Obscure Units Converter
Before the metric system, units were local, trade-specific and often literally part of the landscape. A rod was the length of a surveyor's pole, a furlong was the length of a furrow, and an acre was the area one team of oxen could plough in a day. That is why historical conversions are full of approximate values and regional variants.
Some of these units never disappeared. The acre is still the standard land measure in the United States and the United Kingdom, the troy ounce still prices precious metals, and the stone still describes body weight in Britain and Ireland. Others survive mainly in poetry, heraldry or the names of old measures on pub signs.
Volume is the messiest category. A gallon in the United States is 3.785 litres; an imperial gallon is 4.546 litres, about 20% larger. A US pint is 16 US fluid ounces, while an imperial pint is 20 imperial fluid ounces. A firkin of beer is 9 imperial gallons, but a firkin of mass is 90 pounds. The page keeps these definitions explicit rather than pretending one rule covers every trade.
Use the results as historical approximations, not as legal definitions. Where a unit varied by region or commodity — the arpent, the ell, the cubit — the table gives a common standard and the notes explain the variation. For modern trade, always use the legal unit of the country you are trading in.
How the calculation works
- 1 inch = 2.54 cm; 1 hand = 4 in; 1 span = 9 in; 1 cubit = 18 in; 1 ell = 45 in.
- 1 stone = 14 lb; 1 long hundredweight = 8 stone = 112 lb; 1 firkin = 90 lb.
- 1 troy ounce = 31.1034768 g exactly; 1 troy pound = 12 troy ounces.
- 1 imperial gallon = 4.54609 L; 1 US gallon = 3.785411784 L.
- 1 acre = 4,046.8564224 m² = 43,560 square feet; 1 rood = ¼ acre.
- 1 barn = 10⁻²⁸ m², originally a joke unit for nuclear cross-sections.
Reference values
| Unit | Modern value | Notes |
|---|---|---|
| Barleycorn | 8.47 mm | One third of an inch |
| Hand | 10.16 cm | Four inches; still used for horses |
| Cubit | 45.72 cm | Eighteen inches; Egyptian royal cubit was longer |
| Ell | 1.143 m | 45 inches; varied by country and cloth |
| Rod / perch | 5.0292 m | 16.5 feet |
| Chain | 20.1168 m | 66 feet; ten chains make a furlong |
| Furlong | 201.168 m | One eighth of a mile |
| League | 4.828 km | Usually three miles |
| Stone | 6.35029 kg | Fourteen pounds |
| Troy ounce | 31.1035 g | Precious metals |
| Firkin (mass) | 40.8233 kg | Ninety pounds |
| Firkin (volume) | 40.9148 L | Nine imperial gallons |
| Hogshead | 238.481 L | 63 US gallons |
| Acre | 4,046.86 m² | 43,560 square feet |
| Rood | 1,011.71 m² | Quarter of an acre |
| Hide | 48.5623 ha | About 120 acres |
| Section | 2.59 km² | 640 acres |