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Force Converter

Convert force units using the standard gravity definition value.

Engineering drawings specify kilonewtons, everyday speech talks about kilograms of force, imported equipment is rated in pounds-force — force units mix the gravity habit with the international standard. This tool converts between N, kN, kgf and lbf using the standard gravity definition of 9.80665 N to the kilogram-force; the anchors are 1 kgf ≈ 9.8 N and 1 lbf ≈ 4.45 N.

One thing to keep straight: the kilogram-force is the force a one-kilogram mass experiences under standard gravity, and the "kilos" of workshop speech usually means it, while physics does its arithmetic in newtons. "One kilogram equals 9.8 newtons" is a conversion of force, not of mass — the mass is one kilogram everywhere, and only the gravitational acceleration changes.

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How to use

  1. Enter the force and choose its unit.
  2. Read the value in the other three units.
  3. Use newtons for calculations and kilograms-force for workshop contexts.
  4. Remember that kgf is a force, not a mass.

How it works

Force conversion factors

The SI unit of force is the newton (N) = 1 kg·m/s2. Based on the newton: 1 kN = 1000 N, 1 kgf = 9.80665 N, 1 lbf = 4.4482216152605 N — the first two metric, the last imperial.

The origin of kgf and lbf

kgf (kilogram-force) is the weight of 1 kg under standard gravity; it isn't a round 10 N because the internationally agreed standard gravity is 9.80665 m/s2. lbf (pound-force) works the same way: the weight of 1 pound under standard gravity, about 4.448 N.

Common force magnitudes

Common magnitudes: a 1 kg object weighs about 9.8 N; 1 kN is about 102 kgf, roughly the weight of a 102 kg object; an adult male grip is about 300-500 N, and ground reaction force while running can reach 2-3 times body weight.

Code example

JavaScript The standard gravity definition value 

const G = 9.80665;   // ISO 80000 definition — do not approximate with 9.8
const N = { N: 1, kN: 1e3, kgf: G, lbf: 4.4482216152605 };

const convert = (v, from, to) => v * N[from] / N[to];

convert(1, "kgf", "N");    // 9.80665
convert(75, "kg", "N");    // a 75kg body weighs about 735.5 N

Python The same coefficients in Python 

G = 9.80665
N = {"N": 1, "kN": 1e3, "kgf": G, "lbf": 4.4482216152605}

convert = lambda v, f, t: v * N[f] / N[t]

convert(10, "kN", "tf")    # tonne-force = 1000 kgf, about 1.02

FAQ

Why is 1 kgf 9.80665 N and not 10 N?

kgf is defined as the weight of 1 kg under standard gravity, and the internationally agreed standard gravity is g = 9.80665 m/s2, hence 9.80665 N. Engineering mental math often approximates it to 10 N; use the defined value for precise work.

How is the newton defined?

1 N = 1 kg·m/s2, the force that gives a 1 kg object an acceleration of 1 meter per second squared. It's an SI derived unit, combining the base units of mass, length and time.

How heavy is something under 1 kN?

1 kN is about 102 kgf, roughly the gravity on a 102 kg object. Structural and lifting engineering marks load capacity in kN; read 10 kN as "about a tonne of weight."

Are pound-force (lbf) and pound-mass (lb) the same?

No. lb is mass, lbf is force: 1 lbf is the weight of 1 pound-mass under standard gravity, about 4.448 N. In US material, a load marked just "lb" usually means lbf in practice, but confirm before computing.

About how many newtons can a person exert?

Rough references: adult male grip about 300-500 N, female about 200-350 N; ground reaction force while walking is about 1.2 times body weight (70 kg is about 820 N), reaching 2-3 times while running — useful in rehab training.

Does a bathroom scale show force or mass?

A scale measures pressure (force) and divides by local gravity to display mass, so its unit is kg. Strictly, "weighing 70 kg" is mass; the gravity on it is about 686 N.

Are results recorded anywhere?

No. Conversion uses a single multiply/divide formula, entirely local in your browser, with no upload. History is stored locally — clear it with one click, or use an incognito window for no trace.