The kilogram-force has never been a part of the International System of Units (SI), which was introduced in 1960. The SI unit of force is the Newton.
Prior to this, the unit was widely used in much of the world; it is still in use for some purposes. The thrust of a rocket engine, for example, was measured in kilograms-force in Germany, in the Soviet Union (where it remained the primary unit for thrust in the Russian space program until at least the late 1980s), and it is still used today in China and sometimes by the European Space Agency.
It is also used for tension of bicycle spokes, for Torque measured in "meter-kilograms", for pressure in kilograms per square centimeter, for the draw weight of bows in archery, and to define the "metric Horsepower" (PS) as 75 m·kgf/s.
Grams-force and kilograms-force were never well-defined units until the CGPM adopted a standard acceleration of gravity of 980.665 cm/s² for this purpose in 1901, though they had been used in low-precision measurements of force before that time.
A tonne-force, metric ton-force, or megagram-force is 1000 kilograms-force.
| | Newton (SI unit) | Dyne | Kilopond (kilogram-force) | Pound-force | Poundal | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 N | = 1 kg·m/s² | = 105 dyn | ≈ 0.22481 lbf | ≈ 7.2330 pdl | |||||||
| 1 dyn | = 10−5 N | = 1 g·cm/s² | <td ≈ 1.0197×10−6 kp>≈ 2.2481×10−6 lbf≈ 7.2330×10−5 pdl | ||||||||
| 1 kp | = 9.80665 N | = 980665 dyn | = gn·(1 kg) | <td ≈ 2.2046 lbf>≈ 70.932 pdl|-1 lbf | ≈ 444822 dyn | ≈ 0.45359 kp | = gn·(1 lb) | - | 1 pdl | ≈ 13825 dyn | ≈ 0.014098 kp | <td ≈ 0.031081 lbf>= 1 lb·ft/s²
| The values for the pound-force are calculated using the same value for the standard acceleration ofgravity gn which is official for defining the kilopond (a.k.a. kilogram-force), something which is notrequired. Other values such as gn = 32.16 ft/s² are also used. | |||||||||||