Force Calculator (F = ma)
Solve Newton's second law for force, mass or acceleration.
Results update as you type.
About this calculator
Newton's second law is the cornerstone of classical mechanics: the net force on an object equals its mass times its acceleration, F = m × a. Rearranged, the acceleration a body undergoes is a = F / m, and the mass implied by a known force and acceleration is m = F / a. The result is in newtons (N), the SI unit of force defined as the force that gives a 1 kg mass an acceleration of 1 m/s². This calculator also converts to pound-force and kilogram-force, using 1 N = 0.2248 lbf = 0.1020 kgf.
Choose which quantity to solve for and enter the other two. For example, accelerating a 10 kg mass at 9.8 m/s² takes F = 10 × 9.8 = 98 N — which is also the weight of that mass on Earth, since weight is just the gravitational force m × g. Push a 1,500 kg car to 2 m/s² and you need 3,000 N; halve the mass or the acceleration and the force halves too, because force is directly proportional to both.
Force calculations underpin everything from working out the thrust a rocket needs and the braking force to stop a vehicle, to the tension in a lift cable and the recoil of a firearm. Keep the units consistent — kilograms, metres and seconds give newtons — and remember the law describes the net force: if several forces act, add them as vectors first, then divide by mass to get the actual acceleration.
Frequently asked questions
What is Newton's second law?
It states that the net force on an object equals its mass times its acceleration, F = m × a. Doubling the mass or the acceleration doubles the force.
What is a newton?
A newton is the SI unit of force: the force that gives a 1 kg mass an acceleration of 1 m/s². It equals about 0.2248 pounds-force.
How do I find acceleration from force and mass?
Rearrange the law to a = F / m. A 3,000 N net force on a 1,500 kg car produces 3,000 / 1,500 = 2 m/s² of acceleration. Larger mass means less acceleration for the same force.
Is weight the same as force?
Weight is the specific gravitational force on a mass, W = m × g, with g ≈ 9.81 m/s² on Earth. So a 10 kg mass weighs about 98 N. Mass stays the same everywhere; weight changes with local gravity.
What is the difference between mass and force?
Mass (kilograms) measures how much matter an object contains and resists acceleration; force (newtons) is a push or pull. They are linked by F = m × a but they are different quantities with different units.
What does "net force" mean in the formula?
It is the vector sum of all forces acting on the object. If a 100 N push meets a 30 N friction force, the net force is 70 N, and that is the value that determines the actual acceleration.
How do I convert newtons to pounds-force or kilograms-force?
Multiply newtons by 0.2248 for pounds-force or by 0.1020 for kilograms-force. So 98 N is about 22 lbf or 10 kgf — the calculator shows both conversions automatically.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/force/curl
curl "https://calculator.free/api/v1/force/?solve=force&mass=10&acceleration=9.8"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/force/?" + new URLSearchParams({
"solve": "force",
"mass": "10",
"acceleration": "9.8"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.