Written by Muneeb Rana · Last updated 26 October 2026
Quick answer: A stopping distance calculator adds thinking distance (how far you travel before you react) to braking distance (how far the car takes to stop). Thinking distance grows with speed; braking distance grows with speed squared. That is why going from 30 to 60 mph roughly quadruples braking distance, and why small speed increases matter so much.
TL;DR
- Stopping = thinking + braking.
- Braking distance rises with the square of speed.
- Wet or icy roads multiply it.
- UK Highway Code table included.
- Leave at least a two-second gap.
How the stopping distance calculator works
Thinking distance = speed × reaction time. Braking distance = speed² ÷ (2 × deceleration), the standard physics for constant deceleration. The tool defaults to a 0.67-second reaction time and a dry-road deceleration of about 6.6 m/s², the assumptions that roughly reproduce the UK Highway Code's typical stopping distances. Change them to model a tired driver or a wet road.
Highway Code typical stopping distances
| Speed | Thinking | Braking | Total |
|---|---|---|---|
| 20 mph | 6 m | 6 m | 12 m |
| 30 mph | 9 m | 14 m | 23 m |
| 40 mph | 12 m | 24 m | 36 m |
| 50 mph | 15 m | 38 m | 53 m |
| 60 mph | 18 m | 55 m | 73 m |
| 70 mph | 21 m | 75 m | 96 m |
Figures as published in the Highway Code's typical stopping distances diagram for a car on a dry road.
Why speed matters so much
Doubling speed doubles thinking distance but quadruples braking distance. The WHO notes that every 1% increase in mean speed produces about a 4% increase in fatal crash risk. A few mph over the limit can be the difference between stopping short and hitting someone.
Wet, icy and distracted
The Highway Code advises at least a two-second gap on fast roads, at least doubled on wet roads and up to ten times greater on ice. Distraction adds to reaction time: WHO says drivers using phones are about four times more likely to crash. That is one more reason never to handle a speedometer app while moving.
Use the result wisely
The calculator shows an idealised figure. Real stops depend on tyres, brakes, load, slope and surface. Treat it as a reminder to leave space, not a promise.
Related: Speedometer app safety: how to use it without distraction · Free speed tools · The dangers of speeding · US speed limits explained · MPH to meters per second converter · Phone use while driving laws · Phone mount placement: where to put your phone · Speed limit app: what to look for
Get Speedometer PRO on Google Play · Download on the App Store · Set it up before you move; never handle your phone while driving.
Sources
- The Highway Code, rules 103-158 incl. stopping distances (GOV.UK): gov.uk (accessed 26 October 2026)
- Braking distance (Wikipedia): en.wikipedia.org (accessed 26 October 2026)
- Road traffic injuries fact sheet (World Health Organization): who.int (accessed 26 October 2026)
- Mental chronometry: reaction time (Wikipedia): en.wikipedia.org (accessed 26 October 2026)
FAQ
What is the stopping distance at 60 mph?
The UK Highway Code gives 73 metres on a dry road for a car: 18 m of thinking distance plus 55 m of braking distance.
How does speed affect braking distance?
Braking distance rises with the square of speed, so doubling speed roughly quadruples it, while thinking distance only doubles.
What reaction time does the tool use?
About 0.67 seconds by default, which matches the Highway Code's thinking distances. Real reaction times are often longer, especially when tired or distracted.
How much longer in the wet?
The Highway Code says to at least double your following gap on wet roads and allow up to ten times more on ice.
Is this accurate for my car?
No. It is a physics estimate; your real distance depends on tyres, brakes, load, slope and the road surface.