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# British Imperial System

## A principal system of units.

English units forms the basic for the Imperial system formerly used in the Commonwealth countries and the Customary system used in the US.

The basic difference between dimensional systems are not the units employed but the primary dimensions.

• The SI-system use mass, length and time as primary quantities (mechanics). Other units quantities are secondary. The SI-system is a MLT (mass-length-time) system
• The English system use force, mass, length and time as primary quantities. Other units are secondary. The British Imperial System is a FMLT (force-mass-length-time) system

Note that the use of four, three, two or even one(!) primary quantities is a human choice and not necessary basic nature.

### Imperial Primary Quantities

Imperial primary quantities are expressed in the table below:

Imperial System - Primary Quantities
Primary QuantityDimensionsCommon Units
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

### Imperial Secondary Quantities

Some common imperial secondary quantities are expressed in the table below

Imperial System - Secondary Quantities
Primary QuantityDimensionsCommon Units
Acceleration L / T2 foot per second squared
Area L2 square foot, square yard
acre, square mile
Density M / L3 pounds per cubic foot
Frequency 1/T cycle per second
Impulse F T pound-force second
Momentum ML / T pound foot per second
Power LF / T foot pound-force per second
horsepower
Pressure F / L2 pound-force per square inch
Velocity L / T foot per second
mile per hour, knot
Volume L3 pint, quart, gallon
cubic foot, cubic yard
Work L F foot pound-force

## Related Topics

• ### Basics

The SI-system, unit converters, physical constants, drawing scales and more.

## Related Documents

• ### BSi - Pipe, Tube and Fittings Standards and Specifications

British standards and specifications for pipe, tube and fittings.
• ### Decimal System Prefixes

Prefix names used for multiples and submultiples units.

Radian is the SI unit of angle. Convert between degrees and radians. Calculate angular velocity.
• ### SI System

An introduction to the SI metric system.
• ### Symbols Used to Denote a Chemical Reactions and Process or Condition

Explanation of symbols used as subscripts or superscripts to tell more about the type of chemical reaction, process or condition.
• ### Toluene Liquid - Thermal Properties vs. Temperature

Density, specific heat, thermal conductivity and more.
• ### Unit Converter with commonly used Units

Common converting units for Acceleration, Area, Density, Energy, Energy per unit mass, Force, Heat flow rate, Heat flux, Heat generation per unit volume and many more.
• ### USCS - United States Customary System Units

An overview of the United States Customary System Units - Imperial Units.

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## Citation

• The Engineering ToolBox (2005). British Imperial System. [online] Available at: https://www.engineeringtoolbox.com/british-imperial-system-d_993.html [Accessed Day Month Year].

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