How the Stopping Distance Calculator Works
Stopping distance has two parts that add together.
Thinking distance
The distance you travel while you notice the hazard and move to the brake. It equals speed times reaction time.
Braking distance
The distance the car needs to stop once the brakes are on. It grows with the square of your speed.
Highway Code basis
Dry braking uses about 6.6 m/s² of deceleration, which closely matches the UK Highway Code typical distances.
Rough multipliers
Braking distance is doubled for wet roads and multiplied by ten for icy roads, following Highway Code gap advice.
Typical Stopping Distances by Speed
Figures from the UK Highway Code typical stopping distances chart, dry road, average car.
The Highway Code calls these figures a general guide. Your real distance depends on your attention, the road surface, the weather and the condition of your vehicle.
What Changes Your Stopping Distance
Small changes in speed or attention make a big difference.
Speed
Braking distance grows with the square of speed. Going from 30 to 60 mph roughly quadruples it. Read stopping distance explained.
Reaction time
A surprise hazard can take about 1.5 seconds to react to. See average reaction time while driving.
Your condition
Tiredness, alcohol and phone use all slow reactions. Learn more about sleep and alcohol.
Test yourself
Take the reaction time test or the choice reaction test, which is closer to deciding on the road.
Frequently Asked Questions
Quick answers about stopping distance.
How is stopping distance calculated?
Stopping distance is thinking distance plus braking distance. Thinking distance is your speed multiplied by your reaction time. Braking distance grows with the square of your speed, so doubling your speed makes it about four times longer.
What is the stopping distance at 30 mph?
The UK Highway Code gives a typical stopping distance of 23 metres at 30 mph, made of 9 m thinking distance and 14 m braking distance. That is about six car lengths. Real distances depend on the driver, vehicle and road.
What reaction time does this calculator use?
You choose. The default of 0.67 seconds matches the Highway Code thinking distances. You can also pick 1.5 seconds for a surprise hazard, 2.5 seconds, the value road engineers design for, or enter your own time.
How much longer is stopping distance on wet or icy roads?
The Highway Code says gaps should be at least doubled on wet roads and can need to be up to ten times greater on icy roads. This calculator multiplies braking distance by 2 for wet and 10 for icy as a rough guide.
Can I use my VoltReflex score as my driving reaction time?
Not directly. A screen test measures a simple, expected response with your finger ready. Real driving adds looking, deciding and moving your foot to the brake, so driving reaction times are usually much longer than test scores.
This calculator gives rough estimates for learning only. It is not for legal, insurance or accident reconstruction use. Sources The Highway Code, Rule 126 and typical stopping distances and City of Los Angeles, Safe Stopping Distances