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 g_n ^[1]). It is used primarily in the United States 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[edit]

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 g_n, 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[edit]

• 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[edit]

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[edit]

1. ↑ ^{1.0 1.1} 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.