Measure · 4 units
Force
A force is mass times acceleration; the newton is 1 kg m/s². The kilogram-force and pound-force are the weights of 1 kg and 1 lb under standard gravity, 9.806 65 m/s², a conventional value adopted in 1901.
Convert force
Then and now
Engineering once measured force in kilograms and pounds, which blurs mass and weight; the SI keeps them apart.
All force units
“Exact” means the unit is defined as an exact multiple of the SI unit; the decimal is printed in full when it ends. Rows marked historical or obsolete are kept for reading old documents.
| Unit | Defined as | In SI | Status | Source |
|---|---|---|---|---|
| SI | ||||
| newton N | 1 kg · m/s² | 1 N | exact | BIPM SI Brochure |
| US engineering | ||||
| pound-force lbf | 4.448 221 615 260 5 N (1 lb under standard gravity) | 4.448 221 615 260 5 N | exact | NIST SP 811 |
| Gravitational metric | ||||
| kilogram-force kgf | 9.806 65 N (1 kg under standard gravity) | 9.806 65 N | exact historical | NIST SP 811 |
| CGS | ||||
| dyne dyn | 1 g · cm/s² | 0.000 01 N | exact historical | NIST SP 811 |