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Physical system of measurement that uses the foot, pound, and second as base units
The foot–pound–second system (FPS system) is a system of units built on three fundamental units: the foot for length, the (avoirdupois) pound for either mass or force (see below), and the second for time.

Collectively, the variants of the FPS system were the most common system in technical publications in English until the middle of the 20th century.

When the pound is used as a unit of mass, the core of the coherent system is similar and functionally equivalent to the corresponding subsets of the International System of Units (SI), using metre, kilogram and second (MKS), and the earlier centimetre–gram–second system of units (CGS). This system is often called the Absolute English System. In this sub system, the unit of force is a derived unit known as the poundal. Everett (1861) proposed the metric dyne and erg as the units of force and energy in the FPS system. Latimer Clark's (1891) "Dictionary of Measures" contains celo (acceleration), vel or velo (velocity) and pulse (momentum) as proposed names for FPS absolute units.

The candle and the foot candle were the first defined units of light, defined in the Metropolitan Gas Act (1860). The foot candle is the intensity of light at one foot from a standard candle. The units were internationally recognized in 1881, and adopted into the metric system.

Together with the fact that the term "weight" is used for the gravitational force in some technical contexts (physics, engineering) and for mass in others (commerce, law), and that the distinction often does not matter in practice, the coexistence of variants of the FPS system causes confusion over the nature of the unit "pound". Its relation to international metric units is expressed in kilograms, not newtons, though, and in earlier times it was defined by means of a mass prototype to be compared with a two pan balance which is agnostic of local gravitational differences. In July 1959, the various national foot and avoirdupois pound standards were replaced by the international foot of precisely 0.3048 and the international pound of precisely 0.45359237, making conversion between the systems a matter of simple arithmetic. The conversion for the poundal is given by 1 pdl = 1 lb·ft/s2 = 0.138254954376 (precisely). To convert between the absolute and gravitational FPS systems one needs to fix the standard acceleration g which relates the pound to the pound force. While g strictly depends on one's location on the Earth surface, since 1901 in most contexts it is fixed conventionally at precisely g0 = 9.80665 ≈ 32.17405.