Stopping distances, and how to remember them

Stopping distances come up in the theory test in several forms: the overall distance at a given speed, how far you travel before you even touch the brake, and how much further it takes to stop on a wet or icy road. They're worth learning properly, because they're straightforward marks once you know them.

The typical stopping distances

These are the figures from the Highway Code, for a car in good condition on a dry road with an alert driver.

Thinking distance is how far you travel between seeing a hazard and starting to brake. Braking distance is how far you travel once the brakes are on. Add them together and you get the overall stopping distance.

Stopping distance calculator

Dry-road figures are the Highway Code's typical stopping distances. For wet and icy roads the calculator uses the Highway Code's rules of thumb: at least double on wet roads, and up to ten times on ice.

The pattern behind the numbers

You don't have to learn the table as eighteen separate numbers. There are two patterns that make it much easier.

Thinking distance goes up by 3 metres for every 10 mph

6, 9, 12, 15, 18, 21. If you know one, you know them all. A quick way to get it: take the speed, divide by 10, and multiply by 3. At 50 mph that's 5 × 3 = 15 metres.

This is the part that grows steadily with speed, because your reaction time stays about the same however fast you're going. You simply cover more ground before you react.

Braking distance grows much faster than speed

Double your speed from 30 to 60 mph and the braking distance roughly quadruples, from 14 to 55 metres. That's the physics of it: the energy a car carries rises with the square of its speed. It's also why even a few miles an hour makes a real difference in an emergency.

A trick for the overall figure

For the totals, one memory aid works neatly in feet. Multiply the speed by a number that starts at 2 for 20 mph and goes up by a half for each extra 10 mph:

The test asks in metres, so use the trick as a check rather than as your answer. If you can get the feet figure in your head, the matching metre figure from the table is easier to recall.

Wet and icy roads

The table is for dry roads. The Highway Code says the gap you leave should be at least doubled on wet roads and can need to be up to ten times greater on icy roads. Expect questions that ask how much further it takes to stop in the wet (about twice as far) or on ice (up to ten times as far).

Other things that lengthen stopping distances also come up: worn tyres, worn brakes, a heavily loaded car, driving downhill, and anything that slows your reactions, such as tiredness, alcohol, drugs or using a phone.

The two-second rule

In real driving you can't measure 73 metres on a road, so the Highway Code gives a simpler rule: leave at least a two-second gap between you and the vehicle in front on high-speed roads and in tunnels where visibility is reduced, and at least double it on wet roads.

To check it, watch the vehicle in front pass a fixed point such as a lamp post or bridge. Say "only a fool breaks the two-second rule". If you reach the same point before you finish saying it, you're too close.

Large vehicles and motorcycles need more room to stop, so give them more space as well.

How it's tested

Stopping distance questions tend to fall into a few types:

• What is the shortest overall stopping distance at a given speed on a dry road?
• What is the typical thinking distance at a given speed?
• How much further does it take to stop on a wet or icy road?
• What gap should you leave behind the vehicle in front in good, wet or icy conditions?

If you can write out the table from memory and know the "double in the wet, up to ten times on ice" rule, you'll be able to answer all of them. Our app has a stopping distances learning aid that shows the thinking and braking parts side by side, which some people find easier to remember than a table.

Figures from the Highway Code (rule 126 and the typical stopping distances diagram).