About the Stopping Distance Calculator
A vehicle does not stop the moment the driver sees danger. It first travels the reaction distance, while the driver reacts, and then the braking distance, while the brakes work. This calculator adds the two. You enter the speed, the driver's reaction time and the road surface, and it gives the total stopping distance in metres and feet. Type the speed, the reaction time and the road surface and the stopping distance appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Stopping Distance Calculator
- 1Enter the speed, the reaction time and the road surface.
- 2Pick the units or options from the menus if the stopping distance tool offers them.
- 3Read the stopping distance in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the stopping distance
Drivers and learners use it to understand safe following distances. Teachers use it in road-safety lessons to show why speed limits drop near schools, and engineers use it to place warning signs and set sight distances.
Changing the road surface shows the danger of rain and ice. The same 50 km/h stop on ice, with a friction of 0.1, takes 98 m of braking, and 119 m in total, more than three times the dry figure.
How the stopping distance is worked out
Reaction distance = speed × reaction time. Braking distance = speed² ÷ (2 × friction × g). Total = reaction + braking. At 50 km/h (13.89 m/s) with a reaction time of 1.5 s on dry asphalt (friction 0.7), the car covers 20.8 m before braking starts and then needs 14.1 m to stop: 34.9 m in total. At 100 km/h the total is 97.9 m, nearly three times as far.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Speed in m/s, km/h or mph
- Five road surfaces
- Results in metres and feet
Mistakes to avoid with stopping distance
The friction values are typical, and real braking depends on tyres, brakes, slope and the driver. Anti-lock brakes help but cannot beat the limit of the road. Treat the result as a guide, and always keep more distance than the minimum.
On phone and computer
On a phone, type into the boxes one after another and read the stopping distance underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the stopping distance move. The stopping distance calculator works the same on both. Safe driving depends on speed and energy, so Speed Calculator and Kinetic Energy Calculator help you understand why stopping takes longer at high speed. Mileage Calculator and Fuel Economy Calculator help with trip planning.
Features
- Double the speed, four times the braking
- Wet roads need more room
- Keep extra distance
- Clear messages when the stopping distance inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate stopping distance?
Reaction distance = speed × reaction time. Braking distance = speed² ÷ (2 × friction × g). Total = reaction + braking. At 50 km/h (13.89 m/s) with a reaction time of 1.5 s on dry asphalt (friction 0.7), the car covers 20.8 m before braking starts and then needs 14.1 m to stop: 34.9 m in total. At 100 km/h the total is 97.9 m, nearly three times as far.
What is the formula for stopping distance?
Reaction distance = speed × reaction time. Braking distance = speed² ÷ (2 × friction × g). Total = reaction + braking. The stopping distance calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a normal reaction time?
About 1.5 seconds for an alert driver in good conditions. Tiredness, alcohol, phones and age can raise it.
Why does speed matter so much?
Braking distance grows with the square of speed. Doubling the speed makes the braking distance four times longer.
Does the tool include the slope?
No. Going downhill lengthens the distance, and going uphill shortens it.
Is this stopping distance calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.