The poundforce or simply pound (abbreviations: lb, lbf, or lb_{f}) is a unit of force.
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The poundforce is approximately equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in lowprecision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.^{[1]}
The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. Today, in accordance with the General Conference on Weights and Measures, standard gravity is usually taken to be 9.80665 m/s^{2} (approximately 32.17405 ft/s^{2})^{[2]}^{[3]}
From the acceleration of the standard gravitational field and the international avoirdupois pound, we arrive at the following definition:^{[4]}
1 poundforce  ≡ 1 pound times standard acceleration due to gravity  
≡ 0.45359237 kg × 9.80665 m/s^{2}  = 4.4482216152605 N  
= 32.17405 lb_{m}·ft/s^{2} 
Sixteen avoirdupois ounces (as a unit of mass) are equal to one avoirdupois pound (as a unit of mass). Similarly one ounceforce is equal to a sixteenth of a poundforce.
newton (SI unit) 
dyne  kilogramforce, kilopond 
poundforce  poundal  

1 N  ≡ 1 kg·m/s²  = 10^{5} dyn  ≈ 0.10197 kp  ≈ 0.22481 lb_{f}  ≈ 7.2330 pdl 
1 dyn  = 10^{−5} N  ≡ 1 g·cm/s²  ≈ 1.0197×10^{−6} kp  ≈ 2.2481×10^{−6} lb_{f}  ≈ 7.2330×10^{−5} pdl 
1 kp  = 9.80665 N  = 980665 dyn  ≡ g_{n}·(1 kg)  ≈ 2.2046 lb_{f}  ≈ 70.932 pdl 
1 lb_{f}  ≈ 4.448222 N  ≈ 444822 dyn  ≈ 0.45359 kp  ≡ g_{n}·(1 lb)  ≈ 32.174 pdl 
1 pdl  ≈ 0.138255 N  ≈ 13825 dyn  ≈ 0.014098 kp  ≈ 0.031081 lb_{f}  ≡ 1 lb·ft/s² 
The value of g_{n} as used in the official definition of the kilogramforce is used here for all gravitational units. 
In some contexts, the term "pound" is used almost exclusively to refer to the unit of force and not the unit of mass. In those applications, the preferred unit of mass is the slug, i.e. lb_{f}·s^{2}/ft. In other contexts, the unit "pound" refers to a unit of mass. In circumstances where there may otherwise be ambiguity, the symbols "lb_{f}" and "lb_{m}" and the terms "poundsforce" and "poundsmass" can be used to distinguish.
Three common, equally valid footpoundsecond (fps) systems of units for doing calculations with mass and force are summarized in the table below, which also includes the corresponding metric units.
System  Gravitational  Engineering  Absolute  

Force (F)  F = m·a  F = m·a/g_{c} = w·a/g  F = m·a  
Weight (w)  w = m·g  w = m·g/g_{c} ≈ m  w = m·g  
Units  English  Metric  English  Metric  English  Metric 
Acceleration (a)  ft/s^{2}  m/s^{2}  ft/s^{2}  m/s^{2}  ft/s^{2}  m/s^{2} 
Mass (m)  slug  hyl  poundmass  kilogram  pound  kilogram 
Force (F)  pound  kilopond  poundforce  kilopond  poundal  newton 
In the "engineering" fps system, the weight of the mass unit (poundmass) on Earth's surface is approximately equal to the force unit (poundforce). The price for this convenience is that the force unit is not equal to the mass unit multiplied by the acceleration unit^{[5]}—the use of Newton's Second Law, F = ma, requires another factor, g_{c}, usually taken to be 32.17405 lb·ft/(lbf·s^{2}). The "gravitational" fps system is a coherent system of units: by using the slug as the unit of mass, it avoids the need for such a constant. The "absolute" system is similarly coherent; the SI units are those of the "absolute" metric system.
This value was the conventional reference for calculating the kilogramforce, a unit of force whose use has been deprecated since the introduction of SI.The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980.665 cm/s^{2}, value already stated in the laws of some countries.
The poundforce or simply pound (abbreviations: lb, lb_{f}, or lbf) is a unit of force. The poundforce is about equal to the gravitational force applied on a mass of one pound on the surface of Earth. Since the 18th century, the unit has been used in lowprecision measurements. In the 20th century, people needed a more precise definition. An official value for acceleration due to gravity was needed. Today, in a manner complying with the General Conference on Weights and Measures, standard gravity is usually taken to be 9.80665 m/s^{2} (about 32.17405 ft/s^{2})^{[1]}
The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980.665 cm/s^{2}, value already stated in the laws of some countries.This value was the most common reference for calculating the kilogramforce, a unit of force whose use has been deprecated since the introduction of SI.
