Average Acceleration Calculator
From a starting speed, an ending speed, and the time between them, get the average rate at which an object sped up or slowed down — in metres per second squared.
Three inputs, one answer
Enter the initial velocity, the final velocity, and the time, and the calculator returns the average acceleration in m/s².
Negatives are fine
A negative result just means the object slowed down — deceleration — and velocities themselves may be negative too.
What is average acceleration?
Change in velocity over time
Average acceleration measures how quickly an object's velocity changes over an interval of time. It is the change in velocity — the final velocity minus the initial velocity — divided by how long that change took, written a = (vf − vi) ÷ t. The result is expressed in metres per second squared (m/s²), meaning the velocity changes by that many metres per second for every second that passes. Because it averages over the whole interval, it smooths out any moment-to-moment variation: a car that accelerates hard then eases off still has a single, well-defined average acceleration for the trip.
Enter both velocities in metres per second and the time in seconds to get the average acceleration in m/s² instantly.
One short formula, built from the change in velocity and the elapsed time.
acceleration = (vf − vi) ÷ tFirst find the change in velocity by subtracting the initial velocity (vi) from the final velocity (vf). Then divide that change by the time (t) the change took. Keep velocities in metres per second and the time in seconds, and the answer is in metres per second squared with no conversion needed.
Suppose a car accelerates from rest (0 m/s) to 27.78 m/s — that is 0 to 100 km/h — in 10 seconds.
Change in velocity
27.78 − 0 = 27.78 m/s — the increase in speed over the interval.
Divide by time
27.78 ÷ 10 = 2.778 m/s² — the average acceleration.
Read the result
On average the car gains 2.778 m/s of speed every second for those 10 s.
The sign of the result tells the story. A positive average acceleration means the object sped up over the interval — its final velocity was higher than its initial velocity, as with the car reaching 2.778 m/s². A negative average acceleration means the object slowed down; this is deceleration, and it is a completely valid answer, not an error. Slowing from 50 m/s to a stop in 10 s gives −5 m/s², the minus sign simply pointing to the direction of the change. A result of exactly zero means the velocity was the same at the start and end, so there was no net change in speed over the interval. Remember too that this is the average over the whole interval, not the instantaneous value at any single instant: the real acceleration may have been larger at some moments and smaller at others, yet this figure is the steady rate that would produce the same overall velocity change in the same time. That makes it ideal for comparing vehicle performance, sprint times in sports, or any motion where you care about the overall change rather than the instant-by-instant detail.
The formula is exact, but a couple of practical points are worth keeping in mind.
Average, not instantaneous — and mind your units
This calculator returns the average acceleration over the interval, which can differ from the instantaneous acceleration at any given moment. Keep velocities in metres per second and time in seconds so the answer comes out in m/s²; if your speeds are in km/h, divide by 3.6 first (100 km/h ÷ 3.6 = 27.78 m/s). The time must be greater than zero — a zero interval has no defined acceleration. The tool also assumes you already know the two velocities and the time; it does not work backwards from distance.