Force Calculator (F = ma)
Newton’s second law: enter any two of force, mass and acceleration to get the third, in newtons, kilograms, g, pounds and more.
Answer
F = m × a
- Given (in base units): m = 1,200 kg, a = 3 m/s²
- F = m × a = 3,600 N
Values
Fill in any 2; leave the one to work out empty.
How is this calculated?
F = m × a, so m = F ÷ a and a = F ÷ m. 1 N = 1 kg·m/s²; 1 kgf = 9.80665 N exactly (standard gravity).Runs in your browser — nothing you enter leaves this device.
About this tool
What it does
Force Calculator applies Newton’s second law: the force needed to accelerate a mass is the mass times the acceleration. Enter any two of force, mass and acceleration and the third is worked out, with the formula and the working shown in base SI units. Each value has its own unit, so you can mix them freely: force in newtons, kilonewtons, kilogram-force or pound-force; mass in kilograms, grams, tonnes or pounds; acceleration in metres per second squared, feet per second squared, or multiples of standard gravity (g). That makes everyday questions quick — the force behind a car’s acceleration, how hard a lift cable pulls, how many g a given force gives a payload, or what one kilogram weighs in newtons.
How to use it
- Type two of the three values and choose their units.
- Leave the third empty: it is worked out at once and highlighted.
- Change the unit of the answer to see it another way, for example newtons or kilogram-force.
- Read the working under the answer to check it. Clear all starts again.
Limits and your data
- F = m × a is the net force — the sum of every force on the object. To push a car you also have to overcome friction and air resistance, so the force you must apply is larger than the result.
- It assumes the mass does not change during the push. Rockets, which burn fuel and get lighter, need the rocket equation instead.
- Values are magnitudes: directions are left to you. For forces at angles, split them into components first.
- Standard gravity (9.80665 m/s²) is a defined value; real gravity varies from about 9.78 m/s² at the equator to 9.83 m/s² at the poles, so a weight in newtons differs slightly by place.
- Speeds near the speed of light need relativity; this is the everyday, Newtonian formula.
- The calculation runs in your browser. Nothing you enter is sent or saved.
Questions
How do I convert kilograms to newtons?
A mass of m kilograms weighs m × 9.80665 newtons under standard gravity. Enter the mass, set acceleration to 1 g, and read the force: 1 kg weighs 9.80665 N, which is exactly 1 kgf.
What force does a car need to accelerate?
A 1,200 kg car accelerating at 3 m/s² (0 to 100 km/h in about 9 seconds) needs a net force of 3,600 N — the page opens with this example. The engine must also overcome rolling resistance and drag.
What is a g-force?
Acceleration measured in multiples of standard gravity, 9.80665 m/s². Choose g as the acceleration unit to read or enter it directly.
What is the difference between mass and weight?
Mass is how much matter something has, in kilograms, and is the same everywhere. Weight is the force gravity puts on it, in newtons; on the Moon the same mass weighs about a sixth as much.