Pounds-force to Kilograms-force (lbf to kgf)

1 pound-force equals 0.45359237 kilograms-force exactly.

How to convert pounds-force to kilograms-force

To convert pounds-force to kilograms-force, multiply the number of pounds-force by 0.45359237. This factor is exact. To go the other way, multiply kilograms-force by 2.204622622 (rounded).

kilograms-force = pounds-force × 0.45359237

Example: 10 pounds-force = 4.5359237 kilograms-force.

About these units

Pound-force (lbf)

US & ImperialCurrent unit

Exactly 4.4482216152605 newtons: the weight of a one-pound mass under standard gravity. The US unit of force.

People have used the pound-force since the eighteenth century for low-precision work, long before anyone needed to define it carefully. A pound of material on Earth's surface pulls with about a pound of force, which made it convenient to treat the two as one. The twentieth century demanded a precise definition: one pound-force is the avoirdupois pound, exactly 0.45359237 kg, multiplied by standard gravity of 9.80665 meters per second squared, which comes to about 4.448 newtons.

Because the unit is not simply mass times acceleration in its own system, formulas in English engineering units need a conversion constant of about 32.174 pound-feet per pound-force second squared. A slug, 32.174049 pounds of mass, is what one pound-force accelerates at one foot per second squared. In the US, jet and rocket thrust is often given as pounds of thrust: each Space Shuttle solid rocket booster produced 3,300,000 pounds-force. Earth's gravity varies by up to about half a percent between equator and pole, which low-precision work can ignore.

1 pound-force = 4.448221615 newtons (approximately).

Sources: Wikipedia: Pound (force); NIST Guide to the SI, Appendix B.8: conversion factors

Kilogram-force (kgf)

CGS & old metricTraditional unit (still used in some regions)

Exactly 9.80665 newtons: the weight of one kilogram at standard gravity. Also called the kilopond; still common for torque and force in Asia and older European specs.

Before the newton existed, engineers simply measured force by the weight of a standard mass, and the kilogram-force was that idea made official. Its alternative name, kilopond, comes from the Latin pondus, meaning weight. Its size depended on local gravity until 1901, when the General Conference on Weights and Measures adopted 9.80665 m/s2 as standard gravity, which fixed one kilogram-force at exactly 9.80665 newtons. The newton was proposed in 1913 and accepted in 1948.

A proposal to make the kilogram-force an official unit of force was rejected, and it is deprecated and outside SI. Even so it persists in niche uses: bicycle spoke tension, archery bow draw weight, bond wire strength and Vickers hardness testing. German rocket engineers of the 1940s quoted thrust in it, and Soviet and Russian space programs kept doing so until at least the late 1980s. Metric horsepower is defined from it. One kilogram-force is about 2.20462 pound-force and equals 980,665 dynes.

1 kilogram-force = 9.80665 newtons (exactly).

Sources: Wikipedia: Kilogram-force; NIST SP 811, Appendix B.8 conversion factors

Related conversions

See all force units.