Force Calculator (F = ma)Free online science calculator — instant results, no sign-up
Calculate force from mass and acceleration using Newton's second law.
About the Force Calculator (F = ma)
The Force Calculator (F = ma) calculates net force from mass in kilograms and acceleration in meters per second squared using Newton’s second law. It reports the result in newtons and kilonewtons and displays the formula used. With the default mass of 70 kg and acceleration of 3 m/s², the calculated force is 210 N, or 0.21 kN.
- Mass (kg)
- The mass of the object being accelerated, measured in kilograms (kg), with a default value of 70.
- Acceleration (m/s²)
- The rate at which the object’s velocity changes, measured in meters per second squared (m/s²), with a default value of 3.
Formula and method
F = m × a
- FNet force acting on the object, measured in newtons (N).
- mMass of the object, measured in kilograms (kg).
- aAcceleration of the object, measured in meters per second squared (m/s²).
Multiply mass by acceleration to obtain force in newtons, since 1 N = 1 kg·m/s². Divide the force in newtons by 1,000 to express it in kilonewtons. For the default inputs, F = 70 × 3 = 210 N, and 210 ÷ 1,000 = 0.21 kN.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Mass70 kg
- Acceleration3 m/s²
Results
- Force210 N
- In kilonewtons0.21 kN
- FormulaF = m × a
How to use the Force Calculator (F = ma)
- 1Enter the object’s mass in the Mass (kg) field; use 70 for the default example.
- 2Enter its acceleration in the Acceleration (m/s²) field; use 3 for the default example.
- 3Check that mass is expressed in kilograms and acceleration in m/s² before calculating.
- 4Read the Force output: the default inputs give 210 N.
- 5Read In kilonewtons as 0.21 kN and check the Formula row, F = m × a.
Reading your result
The Force row gives the net force in newtons: 210 N for the default inputs. The In kilonewtons row expresses the same force on a larger unit scale: 0.21 kN, not an additional force. The Formula row shows F = m × a, confirming that the result comes from multiplying mass by acceleration.
Limitations
This calculation assumes constant mass and ordinary Newtonian mechanics in an inertial reference frame. The result is net force, not necessarily a single applied force; friction, gravity, and other forces must be accounted for separately when determining an individual force. A single acceleration input represents a magnitude or one signed directional component, not a full three-dimensional vector. Mass should be positive for a physical object. The tool does not handle variable-mass systems or relativistic effects, and output accuracy depends on the accuracy of the inputs.
Common questions
Why do the default inputs produce 210 N?+
Newton’s second law multiplies the mass of 70 kg by the acceleration of 3 m/s². The product is 210 kg·m/s², which equals 210 N.
Is 0.21 kN different from 210 N?+
No. They describe the same force because one kilonewton equals 1,000 newtons. Dividing 210 N by 1,000 gives 0.21 kN.
Does this calculator give the applied force needed to overcome friction?+
It gives the net force needed for the specified acceleration. If friction opposes motion, an applied force acting along the acceleration must also overcome that friction; you need the other forces to determine the applied force.
Does zero acceleration mean no forces are acting?+
No. For a positive mass, zero acceleration gives zero net force. Individual forces can still act and balance each other, and the object may be at rest or moving at constant velocity.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.