What is the SI unit of force?

The International System of Units (SI) is widely used for trade, science and engineering

The SI unit of force is the newton, symbol N. The base units relevant to force are:

• The metre, unit of length — symbol m
• The kilogram, unit of mass — symbol kg
• The second, unit of time — symbol s

Force is defined as the rate of change of momentum. For an unchanging mass, this is equivalent to mass x acceleration.
So, 1 N = 1 kg m s^-2, or 1 kg m/s².

Historically, there have been a variety of units of force and conversion factors. Some of these are given in the table below. Exact conversions are shown in bold, others are quoted to seven significant figures.

Unit	Symbol	Equivalent SI Value
dyne	dyn	10.0 µN
grain-force	grf	635.460 2 µN
gram-force	gf	9.806 65 mN
poundal	pdl	138.255 0 mN
ounce-force (avdp)	ozf	278.013 9 mN
pound-force	lbf	4.448 222 N
kilogram-force	kgf	9.806 65 N
kilopond	kp	9.806 65 N
sthène	sthène	1.0 kN
kip (= 1 000 lbf)	kip	4.448 222 kN
US ton-force (= 2 000 lbf) (short)	tonf (US)	8.896 443 kN
tonne-force (= 1 000 kgf) (metric)	tf	9.806 65 kN
UK ton-force (= 2 240 lbf) (long)	tonf (UK)	9.964 016 kN

The use of abbreviated forms for large and small numbers is encouraged by the SI system. SI prefixes represent multiples of 10³ or 10^‑3.  

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