# Pound-force

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The pound-force (symbol: lbf[note 1] ) is a measurement unit of force which will accelerate 1 pound of mass to 9.80665 m/s2 (≈ 32.17405 ft/s2), the standard average acceleration due to gravity on Earth's surface (referred to as gn[1]). It is used primarily in the United States of America and is equivalent to exactly 4.4482216152605 newtons.[2]

In common usage and other contexts, it is most often referred to in the United States as a pound or as lb, but this can lead to confusion with the pound-mass.

## Definition in terms of the SI unit of force

The newton (symbol: N) is the unit of force named in the International System of Units (SI). Using the standard average acceleration due to gravity, denoted gn, as being 9.80665 m/s2 and the internationally agreed upon definition of the pound-mass, denoted as lbm, as being 0.45359237 kg,[1][3] we can determine the number of newtons exactly equivalent to a pound-force:

{\displaystyle {\begin{aligned}1\,\mathrm {lbf} &\equiv 1\,\mathrm {lbm} \cdot g_{n}\\&\equiv 0.45359237\,\mathrm {kg} \cdot 9.80665\,\mathrm {{m}/{s^{2}}} \\&\equiv 4.4482216152605\,\mathrm {N} \end{aligned}}}

## Equivalent units of force

• 1 lbf ≈ 4.448221 newton (symbol: N)
• 1 lbf ≈ 4448822 dyne (symbol: dyn)
• 1 lbf ≈ 0.453592 kilogram-force (symbol: kgf)
• 1 lbf ≈ 0.453592 kilopond (symbol: kp)[note 2]
• 1 lbf ≈ 4.448221×10−3 sthène (symbol: sn)
• 1 lbf ≈ 32.17405 poundal (symbol: pdl)
• 1 lbf ≡ 0.001 kip (symbol: kip)[note 3]

## Notes

1. The symbol lbf is derived from the Latin libra for "pound" and the symbol f for "force")
2. Another name for a kilogram-force. Not to be confused with "kilopounds", meaning 1,000 pounds of mass.
3. A non-SI unit of force equal to 1,000 pound-force.

## References

1. Resolution of the 3rd meeting of the CGPM (1901) Definition of the standard average acceleration due to gravity
2. Metric Conversion Table Scroll down to "Force"
3. Appendix 8, Customary System of Weights and Measures U.S. Dept. of Commerce, July 15, 1968. Definition of the pound-mass.