Acceleration Calculator
Pick how you know the acceleration: from how fast the speed changes, or from the force on an object of a given mass. A negative answer means slowing down.
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Formula
- From speed:
a = (v − u) ÷ t, where u is the initial speed, v the final speed and t the time. - From force:
a = F ÷ m(Newton's second law, F is the net force).
Speeds are converted to m/s (1 km/h = 1 ÷ 3.6 m/s, 1 mph = 0.44704 m/s, 1 ft/s = 0.3048 m/s), force to newtons (1 lbf = 4.4482216152605 N) and mass to kilograms (1 lb = 0.45359237 kg). One g is 9.80665 m/s².
Worked example
A car goes from 0 to 100 km/h in 4.5 s. 100 km/h = 27.7778 m/s, so a = 27.7778 ÷ 4.5 = 6.1728 m/s², which is 0.6295 g or 20.252 ft/s².
A net force of 1000 N on 800 kg: a = 1000 ÷ 800 = 1.25 m/s².
Frequently asked questions
What is the acceleration formula?
Acceleration is the change in speed divided by the time taken, a = (v − u) / t. Going from 0 to 100 km/h (27.78 m/s) in 4.5 s gives 27.78 ÷ 4.5 = 6.17 m/s².
How do I find acceleration from force and mass?
Use Newton's second law, a = F / m. A net force of 1000 N on an 800 kg car gives 1000 ÷ 800 = 1.25 m/s². The force must be the net force after friction and drag are subtracted.
What does a negative acceleration mean?
It means the speed is falling (deceleration), or that the object is speeding up in the negative direction. Slowing from 30 m/s to 10 m/s in 4 s gives (10 − 30) ÷ 4 = −5 m/s².
How many g is an acceleration?
Divide by standard gravity, 9.80665 m/s². An acceleration of 6.17 m/s² is 6.17 ÷ 9.80665 = 0.63 g.