The foot, pound, second (fps) system of units is widely-used, particularly in the UK and the USA, in many industries and in most public transactions. When SI units are used, fps units are often offered as an alternative. In this section, fps units are listed and conversion factors relevant to heat and mass transfer are tabulated.

The **foot**, ft, is one third of the **Imperial Standard yard**, yd, which is defined as 0.9144 meter exactly. The foot is therefore 0.3048 meter.

The **pound**, 1b, is defined as 0.453 592 37 kilogram.

The **gallon**, gal, is a unit of volume. The British gallon is defined as the volume of 10 Ibs of water of density 988.859 kg/ m^{3} weighed in air with a density of 1.217 kg/m^{3} against weight of density 8 136 kg/m^{3}, i.e., 1 gal = 4.546 09 × 10^{−3} m^{3}. The US gallon is smaller than the British; 1 USA gallon = 3.785 412 × 10^{−3} m^{3} = 0.8327 gal.

Table 1 gives a list of the most common secondary units in the British System, and Table 2 lists factors for converting fps units to SI units and vice-versa. (See Table 2 on pages 244 and 245.)

**Table 1. Secondary units in the British FPS system**

Units of Length | |

12 inches | = 1 foot (ft) |

3 feet | = 1 yard (yd) |

22 yards | = 1 chain |

10 chains | = 1 furlong |

8 furlongs or 1760 yards | = 1 mile (mi) |

6080 feet | = 1 UK nautical mile* |

6 feet | = 1 fathom |

Units of Mass | |

16 ounces (oz) | = 1 pound (lb) |

14 pounds (lb) | = 1 stone |

28 pounds | = 1 quarter |

4 quarters or 112 pounds | = 1 hundredweight |

20 hundredweight (cwt) or 2240 lb | = 1 ton |

Units of Area | |

4840 square yards | = 1 acre |

640 acres | = 1 square mile |

Units of Volume | |

20 fluid ounces (fl. oz) | = 1 pint |

2 pints (pt) | = 1 quart |

4 quarts (qt) | = 1 gallon |

#### REFERENCES

Taborek, J. (1984) *Heat Exchange Design Handbook*, Hemisphere Publishing Corp.