🧪 Cult units
FFF System Converter
The FFF system measures length in furlongs, mass in firkins and time in fortnights. Pick a quantity, enter a value and convert between FFF units and familiar ones.
About the FFF System Converter
The FFF system is a tongue-in-cheek measurement system built from three traditional English units: the furlong (201.168 m), the firkin (40.8233133 kg, or 90 pounds) and the fortnight (1,209,600 seconds, or 14 days). It is the natural home of the furlong per fortnight, a speed of about 0.166 millimetres per second that is almost exactly one inch per fortnight.
The joke has a serious edge. Physicists use FFF-style units to check dimensional analysis, because a calculation that only works in one arbitrary unit system is usually wrong. Expressing a result in furlongs, firkins and fortnights forces you to track dimensions instead of memorising conversion factors.
Derived FFF units are where the system becomes entertaining. Firkin per furlong is a linear density of about 0.203 kg/m. Firkin furlong squared per fortnight squared is an energy of about 1.13 microjoules. Firkin furlong squared per fortnight cubed is a power of about 0.93 picowatts. The attoparsec per microfortnight is a genuine engineering joke unit: it is about 2.55 cm/s, or roughly one inch per second.
Every conversion on this page passes through SI base units, so there is no accumulated rounding between FFF units. Choose a quantity, select the unit you have and the unit you want, then press Convert. The table underneath shows the same value in every unit in that category.
How the calculation works
- 1 furlong = 201.168 m exactly, or one eighth of a mile.
- 1 firkin = 90 lb = 40.8233133 kg when used as a mass; as a volume it is 9 imperial gallons (40.91481 L).
- 1 fortnight = 14 days = 1,209,600 s.
- 1 furlong per fortnight = 201.168 ÷ 1,209,600 = 0.0001663095 m/s.
- 1 firkin furlong² per fortnight² = 40.8233133 × 201.168² ÷ 1,209,600² = 1.129126 × 10⁻⁶ J.
Reference values
| FFF unit | SI value | Everyday equivalent |
|---|---|---|
| 1 furlong | 201.168 m | About 220 yards |
| 1 firkin (mass) | 40.8233 kg | 90 pounds |
| 1 firkin (volume) | 40.9148 L | 9 imperial gallons |
| 1 fortnight | 1,209,600 s | 14 days |
| 1 furlong/fortnight | 0.00016631 m/s | 0.599 mm/h |
| 1 firkin/furlong | 0.20293 kg/m | About 0.2 kg per metre |
| 1 attoparsec/microfortnight | 0.025510 m/s | About 1 inch per second |
| 1 firkin·furlong²/fortnight² | 1.129126 µJ | A tiny energy |