Driving · Speed & reaction time
Stopping Distance Calculator
How far does a car travel before it stops? Enter your speed, how quickly you react and the road conditions to see your thinking distance, braking distance and total stopping distance — in metres, feet and car lengths.
Total stopping distance
23 m75 ft · ~6 About {lengths} car lengths
- Thinking distance
- 9 m
- Braking distance
- 14 m
At this speed, every extra 0.1 s of reaction adds distance before your foot touches the pedal.
Take a reaction time test to populate your real personal reaction time here. Reaction Time Test.
- Any speed in mph or km/h
- Your own reaction time
- Dry, wet and icy roads
- Matches Highway Code figures
How it works
How Stopping Distance Is Calculated
How far does a car travel before it stops? Enter your speed, how quickly you react and the road conditions to see your thinking distance, braking distance and total stopping distance — in metres, feet and car lengths.
Thinking Distance
Distance covered during biological driver reaction time (speed × reaction time).
Braking Distance
Physical distance car slides under friction deceleration (speed² ÷ 2a).
Total Stopping Distance
Sum of thinking and braking distance.
Highway Code
Stopping Distances at Standard Speeds
Official UK Highway Code (Rule 126) baseline figures for dry asphalt assuming ~0.67 s reaction.
| Speed | Thinking Distance | Braking Distance | Total Stopping Distance | Car Lengths |
|---|---|---|---|---|
| 20 mph (32 km/h) | 6 m (20 ft) | 6 m (20 ft) | 12 m (40 ft) | 3 |
| 30 mph (48 km/h) | 9 m (30 ft) | 14 m (45 ft) | 23 m (75 ft) | 6 |
| 40 mph (64 km/h) | 12 m (40 ft) | 24 m (80 ft) | 36 m (120 ft) | 9 |
| 50 mph (80 km/h) | 15 m (50 ft) | 38 m (125 ft) | 53 m (175 ft) | 13 |
| 60 mph (97 km/h) | 18 m (60 ft) | 55 m (180 ft) | 73 m (240 ft) | 18 |
| 70 mph (113 km/h) | 21 m (70 ft) | 75 m (245 ft) | 96 m (315 ft) | 24 |
Physics
Why Braking Distance Quadruples When You Double Speed
Kinetic energy grows with the square of velocity: Ek = ½mv².
Kinetic Energy Dissipation
Because kinetic energy is proportional to speed squared, doubling speed from 30 to 60 mph multiplies kinetic energy by four, requiring four times the braking distance.
Road Surface Friction
Dry asphalt offers friction coefficients around 0.7–0.8. Wet roads reduce this by 50% (doubling braking distance), while ice reduces friction by 90% (multiplying stopping distance by 10).
Variables
Factors That Worsen Stopping Distance
Driver Distraction
Texting or checking phone screens increases reaction time to 1.5–2.0 seconds, adding 30+ meters of blind travel.
Tire Tread Depth
Worn tires with less than 3mm of tread suffer severe aquaplaning in rain, doubling stopping distance.
Brake Fade & Weight
Heavily loaded passenger vehicles or hot brakes exhibit reduced deceleration force.
FAQ
Stopping Distance Calculator FAQ
What is the formula for calculating stopping distance?
What is the stopping distance at 30 mph?
What is the stopping distance at 70 mph?
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