About the Kinematics Calculator
Kinematics Calculator solves problems of motion in a straight line with constant acceleration. Fill in any three of the five quantities, displacement s, starting speed u, final speed v, acceleration a and time t, leave the other two empty and the page finds them with the SUVAT equations. It shows both answers when the maths gives two real solutions, such as a ball thrown upwards that passes the same height twice, and it explains clearly when the three values you chose cannot happen. It suits physics homework, driving and braking questions and falling objects.
Updated October 2026
How to use the Kinematics Calculator
- 1Fill in exactly three boxes and leave the other two empty.
- 2Use consistent units, such as metres, seconds and metres per second.
- 3Read the two missing values, with every quantity listed.
- 4If two answers appear, think about which one fits your situation.
- 5Copy the result.
What constant acceleration means
Many everyday motions are close to constant acceleration: a car that brakes steadily, a stone that falls, a train that leaves a station. The speed changes by the same amount every second. For these, the five SUVAT quantities are linked by equations, and knowing three of them is enough to find the others.
Choosing signs
Pick a direction as positive and keep to it. If you take up as positive, a falling or thrown object has an acceleration of about −9.8 m/s². A car that slows down while moving forward has a negative acceleration. A wrong sign is the most common cause of a wrong answer, so check that your result makes sense.
- Dropped object: u = 0, a = 9.8 (down is positive)
- Car braking from 20 m/s to rest in 4 s: u = 20, v = 0, t = 4, so a = −5 m/s²
- Ball thrown up at 15 m/s: u = 15, a = −9.8
When two answers appear
If you know u, a and s, the final speed v can be positive or negative because v² is the same either way. That is the situation of an object moving out and coming back. Read the question to see which one fits, and discard the one that does not.
Related tools
Convert units with the Speed Converter and the Acceleration Converter, find free-fall results with the Free Fall Calculator and trajectories with the Projectile Motion Calculator. The Force Calculator links acceleration to force.
Features
- Any three of s, u, v, a, t
- Solves the other two
- Shows both roots when there are two
- Clear errors for impossible combinations
- Works for falling and braking problems
- Private: nothing is uploaded
Frequently asked questions
What are the SUVAT equations?
Five equations for constant acceleration: v = u + at, s = ut + ½at², v² = u² + 2as, s = ½(u + v)t and s = vt − ½at². Each leaves out one of the five quantities.
What do s, u, v, a and t mean?
s is displacement, u the starting (initial) speed, v the final speed, a the acceleration and t the time.
Why must I enter exactly three values?
Three values fix the motion. With two, there are not enough facts, and with four or five the system is over-determined and could disagree.
Why do I sometimes get two answers?
Some problems give a quadratic equation, for example a ball thrown up reaches the same height on the way up and on the way down. Both are valid solutions of the equations.
What if time comes out negative?
A negative time would be before the motion started, so the page leaves that solution out.
What value do I use for gravity?
Free fall near the surface of the Earth has a = 9.8 m/s² downwards (9.81 is more exact). Use a negative a if you take upwards as positive.
Does it work for non-constant acceleration?
No. If the acceleration changes, these equations do not apply.
Is my data stored?
No. It is solved in your browser.