What next?
Force feeds almost every other mechanics calculation.
How to use this calculator
- Enter the mass in kilograms.
- Enter the acceleration in m/s².
- Read the force in newtons.
What your result means
Force is mass times acceleration (Newton’s second law), in newtons — one newton accelerates one kilogram at one metre per second squared. For an object’s weight, use 9.81 m/s² as the acceleration due to gravity.
Why this one is different
The formula is shown with your own numbers dropped into it, so the answer can be checked at a glance rather than trusted: mass times acceleration, then the same force in kilogram-force and pound-force for anyone working in older units. A negative mass is called out as arithmetic rather than physics, and a negative acceleration is named as the deceleration it is.
Why a feather and a hammer fall at the same rate
Newton’s second law — force equals mass times acceleration — underpins everything from rocket launches to car crashes. It also explains the famous experiment: strip away air resistance and everything accelerates under gravity identically, feather and hammer alike.
Once you can link mass, acceleration and force, you can estimate the push behind anything that moves, speeds up or stops.
How it works
Newton's second law states that force equals mass times acceleration. A larger mass, or a greater acceleration, needs a bigger force. Weight is just this law applied with gravitational acceleration (about 9.81 m/s² on Earth).
Formula
Worked example
A 1,500 kg car accelerating at 3 m/s²:
F = 1,500 × 3
F = 4,500 N (4.5 kN)
The same 4,500 N applied to a 3,000 kg vehicle would produce half the acceleration — force scales with mass for a fixed acceleration.
Frequently asked questions
What is a newton?＋
One newton is the force needed to accelerate a 1 kg mass at 1 m/s². Roughly the weight of a small apple.
How do I find my weight in newtons?＋
Enter your mass in kg and use the gravity button — the newton result is your weight as a force.
What is the difference between mass and weight?＋
Mass is how much matter an object contains, measured in kilograms, and it does not change with location. Weight is the force gravity exerts on that mass, measured in newtons: multiply the mass by 9.81 on Earth. A 70 kg person has a weight of about 687 N here and roughly a sixth of that on the Moon.
What is the difference between mass and weight in practice?＋
Mass in kilograms is the same everywhere; weight is the force gravity exerts on it, so it changes with location. A 70 kg person weighs about 687 N on Earth and around 114 N on the Moon.
How do friction forces fit in?＋
Friction opposes motion and is roughly the normal force times a coefficient that depends on the surfaces. It is why the force needed to start something sliding is usually greater than the force to keep it going.
What does net force actually tell me?＋
Only the net force accelerates an object. Equal and opposite forces cancel, which is why a heavy object at rest on a table has large forces acting on it and no acceleration at all.
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Assumptions & limitations
Engineering formulas are exact; the situations they model are not. Read your result with these limits in mind:
- Uses Newton's second law for constant mass — it does not apply to systems losing mass, such as a rocket burning fuel.
- Gives the net force. Friction, drag and gravity must be added or subtracted separately to find what a motor or muscle actually has to supply.
- Assumes an inertial (non-accelerating) frame of reference and speeds well below the speed of light.
- Mass must be in kilograms and acceleration in m/s². Entering grams gives an answer 1,000 times too small.