How do you calculate force?

Multiply the mass in kilograms by the acceleration in m/s². A 2 kg ball accelerating at 3 m/s² experiences 6 N. Enter both above; the page converts to kN, lbf and kgf and shows the weight for comparison.

How much force does gravity exert on a mass?

Its weight, m × g: 70 kg × 9.81 = 687 N on Earth. Enter 9.81 as the acceleration to get any mass's weight; on the Moon use 1.62, on Mars 3.72.

How do I find acceleration from force and mass?

Divide: a = F ÷ m. A 500 N push on a 50 kg crate gives 10 m/s² (before friction). This page multiplies; for the division just rearrange, or run it with trial accelerations.

What is a newton in everyday terms?

About the weight of 100 g — an apple. A kilonewton is the weight of a 102 kg mass. A car engine's push at the wheels is a few thousand newtons; a rocket's thrust, millions.

What is the difference between newtons, kgf and lbf?

The newton is the SI unit of force. A kilogram-force is the weight of 1 kg under standard gravity, 9.80665 N; a pound-force is the weight of 1 lb, 4.4482 N. The page gives all three.

How much force does it take to lift something?

At least its weight, m × 9.81, just to hold it up; to raise it with an upward acceleration a, m × (9.81 + a). Lifting 20 kg at 1 m/s² takes 20 × 10.81 = 216 N.

Force Calculator (Newton's Second Law, F = ma)

Net force from mass and acceleration in newtons, kN, pounds-force and kgf, compared with the object's weight.

Inputs

Mass(kg)

0.001 kg1,000,000,000 kg

Acceleration(m/s²)

-1,000,000 m/s²1,000,000 m/s²

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Force

98 N

Working: 10 kg × 9.8 m/s² = 98 N
In kN, lbf and kgf: 0.098 kN = 22.031 lbf = 9.993 kgf
Weight of the mass on Earth: 98.07 N — this force is 0.999 times that

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What each Force input means

Mass: The object's mass in kilograms — not its weight in newtons or pounds-force. Pounds of mass × 0.4536 give kilograms.
Acceleration: The acceleration in m/s². Enter 9.81 for an object's weight on Earth, a value from the acceleration calculator, or a negative number for braking.

Force formula

F = m × a (kg × m/s² = newtons) · weight = m × g = m × 9.80665 · 1 N = 0.2248 lbf = 0.10197 kgf

\vec{F}_{\text{net}} = m\vec{a}

Newton's second law says the net force on an object equals its mass times its acceleration. One newton is the force that accelerates one kilogram at one metre per second per second — about the weight of a small apple. Enter a mass and an acceleration and the page gives the force in newtons, then in kilonewtons, pounds-force and kilograms-force, and compares it with the object's weight on Earth (mass × 9.81), because 'how many g' is the intuitive way to feel a force. The law works in both directions: a known force on a known mass produces a = F ÷ m, and the acceleration calculator on this site finds a from velocities and time so it can be fed in here.

Force worked example

10 kg accelerating at 9.8 m/s² — the acceleration of free fall — needs 10 × 9.8 = 98 N, which is exactly its weight: gravity is the force that gives it that acceleration. In other units that is 0.098 kN, 22.0 lbf or 10.0 kgf. Pushing a 1,200 kg car at 2 m/s² takes 2,400 N, a fifth of its weight.

More Force examples

A 1,200 kg car accelerating at 2 m/s²: 1,200 × 2 = 2,400 N of net force at the tyres, about a fifth of the car's own weight.

A 70 kg astronaut on the Moon, where gravity is 1.62 m/s²: 70 × 1.62 = 113.4 N — the same mass, weighing about a sixth of the 686 N it weighs on Earth.

Where the Force calculator can give the wrong answer

F = ma is about the net force — the sum of all forces. A 2,400 N push on a car with 400 N of rolling resistance gives 2,000 N net and 1.67 m/s², not 2.
Mass is not weight. A 10 kg object weighs 98 N on Earth and 16 N on the Moon but is 10 kg in both places; enter kilograms, not newtons or pounds-force.
Pounds are ambiguous: pound-mass (0.4536 kg) and pound-force (4.448 N) are different quantities. The page's lbf line is force.
The law holds for constant mass at everyday speeds. A rocket burning fuel changes mass, and relativistic speeds change the relationship.
A negative acceleration gives a negative force — the same size, opposite direction — which is correct for braking.

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Force reference table

What a 70 kg mass weighs on other worlds
Body	Surface gravity	Weight of 70 kg	Feels like on Earth
Earth	9.8 m/s²	686 N	70 kg
Moon	1.6 m/s²	112 N	11.4 kg
Mercury	3.7 m/s²	259 N	26.4 kg
Mars	3.7 m/s²	259 N	26.4 kg
Venus	8.9 m/s²	623 N	63.5 kg
Jupiter (at the cloud tops)	23.1 m/s²	1,617 N	164.9 kg

Source: Surface gravity from NASA's Planetary Fact Sheet (metric, at the equator, including rotation); weight = 70 kg × g

Force FAQ

: Multiply the mass in kilograms by the acceleration in m/s². A 2 kg ball accelerating at 3 m/s² experiences 6 N. Enter both above; the page converts to kN, lbf and kgf and shows the weight for comparison.
: Its weight, m × g: 70 kg × 9.81 = 687 N on Earth. Enter 9.81 as the acceleration to get any mass's weight; on the Moon use 1.62, on Mars 3.72.
: Divide: a = F ÷ m. A 500 N push on a 50 kg crate gives 10 m/s² (before friction). This page multiplies; for the division just rearrange, or run it with trial accelerations.
: About the weight of 100 g — an apple. A kilonewton is the weight of a 102 kg mass. A car engine's push at the wheels is a few thousand newtons; a rocket's thrust, millions.
: The newton is the SI unit of force. A kilogram-force is the weight of 1 kg under standard gravity, 9.80665 N; a pound-force is the weight of 1 lb, 4.4482 N. The page gives all three.
: At least its weight, m × 9.81, just to hold it up; to raise it with an upward acceleration a, m × (9.81 + a). Lifting 20 kg at 1 m/s² takes 20 × 10.81 = 216 N.