British Imperial System

A principal system of units used in Commonwealth countries and the US. The British Imperial System is a FMLT (force-mass-length-time) system with four primary quantities, unlike the SI system which uses only three (MLT).

British Imperial System Overview

The British Imperial System is based on four primary quantities:

Force (F): pound-force
Mass (M): ounce, pound, slug, ton
Length (L): inch, foot, yard, rod, chain, furlong, mile
Time (T): second, minute, hour, day

This differs from the SI system which uses only three primary quantities (mass, length, time).

Common Conversions

Calculator

Inputs

Length (feet)

Mass (pounds)

Velocity (ft/s)

Force (lbf)

Results

Length (Metric)-- meters

Mass (Metric)-- kilograms

Velocity (Metric)-- m/s

Force (Metric)-- newtons

Momentum-- lb·ft/s

Pressure-- psi

Quantity	Dimensions	Common Imperial Units	SI Equivalent
Force	F	pound-force (lbf)	newton (N)
Mass	M	pound (lb), slug	kilogram (kg)
Length	L	foot (ft), mile (mi)	meter (m)
Time	T	second (s), hour (h)	second (s)
Velocity	L/T	foot per second (ft/s), mph	meter per second (m/s)
Acceleration	L/T²	foot per second squared	meter per second squared
Area	L²	square foot (ft²), acre	square meter (m²)
Volume	L³	cubic foot (ft³), gallon	cubic meter (m³)
Density	M/L³	pounds per cubic foot	kilograms per cubic meter
Pressure	F/L²	pound-force per square inch (psi)	pascal (Pa)
Momentum	ML/T	pound foot per second	kilogram meter per second
Impulse	FT	pound-force second	newton second
Power	LF/T	horsepower (hp), ft·lbf/s	watt (W)
Work	LF	foot pound-force (ft·lbf)	joule (J)
Frequency	1/T	cycle per second	hertz (Hz)