Acceleration
Solve average and constant-acceleration problems. Free online calculator with formulas and step-by-step solutions.
Key formula
a = (v - u) / t
How do you calculate acceleration?
Average acceleration is a = (v − u) / t. Subtract initial velocity from final velocity, then divide by time. Rearrange to v = u + at, u = v − at, or t = (v − u)/a. A negative a means the object is slowing down in the positive direction (deceleration).
About this tool
Acceleration is the rate of change of velocity. This page keeps a = (v − u)/t visible so you can solve for acceleration, final speed, initial speed, or time without mixing units or dropping deceleration signs.
How to use this calculator
- Choose the variable you want to solve for and confirm which values are already known.
- Enter inputs in consistent units before calculating so the formula is applied correctly.
- Check whether the result is physically reasonable by comparing it with the size of the inputs.
- Use the step-by-step breakdown to see how the equation was rearranged and evaluated.
Worked examples
Example 1: 0 to 20 m/s in 5.0 s
a = (v − u)/t = (20 − 0)/5.0 = 4.0 m/s² in the direction of motion.
Example 2: braking from 25 m/s to 5.0 m/s
t = 4.0 s. a = (5 − 25)/4 = −5.0 m/s². Magnitude of deceleration is 5.0 m/s².
Example 3: find final velocity
u = 10 m/s, a = 2.0 m/s², t = 6.0 s. v = u + at = 10 + 12 = 22 m/s.
Frequently asked questions
What is the acceleration formula?
Average acceleration is a = (v − u)/t, where v is final velocity, u is initial velocity, and t is time. Units are m/s² when v and u are in m/s and t is in seconds.
What is the difference between acceleration and velocity?
Velocity is how fast you move and in which direction. Acceleration is how quickly that velocity changes. You can have high speed and zero acceleration if velocity stays constant.
What does negative acceleration mean?
With a chosen positive direction, negative a means velocity is decreasing in that direction — often called deceleration or braking. It does not automatically mean the object is moving backward.
How do I convert km/h for acceleration?
Divide km/h by 3.6 to get m/s before using a = (v − u)/t. Leaving km/h mixed with seconds gives a wrong answer.
When should I use SUVAT instead of a = (v − u)/t?
Use a = (v − u)/t when you have (or need) only those three quantities. When displacement s is also involved under constant acceleration, use the kinematics calculator and the full SUVAT set.