Stopping distances for cars when driving is a calculation based on the driver’s thinking distance; the distance the car has traveled before the driver reacts to a hazard and the braking distance, which is how long the car takes to stop once the brakes have been applied.
What affects stopping distance
Thinking distance and Braking distance affect overall stopping distance and both the thinking distance and braking distance can be affected depending on various circumstances.
It’s these circumstances that affects stopping distances of a car. What affects the overall stopping distance of a car is as follows:
Thinking distance
Thinking distances is dependent on the driver and other than the speed at which the vehicle is traveling, can be increased (taking longer to react) by:
- tiredness,
- drink or drug (legal or illegal).
- age – an aging driver may also have an increased thinking distance
- lack of concentration. Such as the use of mobile phones whilst driving
- bad vision can decrease reaction distance
Braking distance
Other than the speed at which a vehicle is traveling, braking distance is affected and can be increased by:
- the weight of the car
- condition of the brakes. Worn discs and/or pads can take longer to reduce a cars speed.
- condition of tyres. Highly worn tyres can increase braking distance, especially during wet weather.
- Wet or icy roads will increase braking distance.
- Road surface condition. General condition of the road surface and how well maintained it is. Gravel, dirt and mud will increase braking distance.
Stopping distances graph
The stopping distance graph below gives a visual representation of the increase in braking distance the faster a vehicle travels. The braking distance in blue is doubled for wet conditions and is multiplied by 10 in icy conditions.
Stopping distances chart in feet
The following stopping distance chart is based on a typical car, in good, legal condition, good weather and on dry well maintained roads. The following chart is for stopping distances in feet based on UK speed limits.
| Thinking distance | Braking distance | Stopping distance |
|---|---|---|
| Thinking distance 20mph: 20 ft. | Braking distance 20mph: 20 ft. | Stopping distance 20mph: 40 feet |
| Thinking distance 30mph: 30 ft. | Braking distance 30mph: 45 ft. | Stopping distance 30mph: 75 feet |
| Thinking distance 40mph: 40 ft. | Braking distance 40mph: 80 ft. | Stopping distance 40mph: 120 feet |
| Thinking distance 50mph: 50 ft. | Braking distance 50mph: 125 ft. | Stopping distance 50mph: 175 feet |
| Thinking distance 60mph: 60 ft. | Braking distance 60mph: 180 ft. | Stopping distance 60mph: 240 feet |
| Thinking distance 70mph: 70 ft. | Braking distance 70mph: 245 ft. | Stopping distance 70mph: 315 feet |
Stopping distances chart in metres
As above, the following chart is based on a typical car, with legal tyres, good brakes and good weather / dry roads. The following chart is for stopping distances in metres based on UK speed limits.
| Thinking distance | Braking distance | Stopping distance |
|---|---|---|
| Thinking distance 20mph: 6 m. | Braking distance 20mph: 6 m. | Stopping distance 20mph: 12 metres |
| Thinking distance 30mph: 9 m. | Braking distance 30mph: 14 m. | Stopping distance 30mph: 23 metres |
| Thinking distance 40mph: 12 m. | Braking distance 40mph: 24 m. | Stopping distance 40mph: 36 metres |
| Thinking distance 50mph: 15 m. | Braking distance 50mph: 38 m. | Stopping distance 50mph: 53 metres |
| Thinking distance 60mph: 18 m. | Braking distance 60mph: 55 m. | Stopping distance 60mph: 73 metres |
| Thinking distance 70mph: 21 m. | Braking distance 70mph: 75 m. | Stopping distance 70mph: 96 metres |
Stopping distances formula
(speed) ² ÷ 20 + thinking distance = overall stopping distance in feet
For stopping distance formula in metres, multiply the result by 0.3
Stopping distance in rain
Due to significantly reduced friction between the tyres and road surface, the above stopping distances are multiplied by 2 for stopping distances in rain.
Stopping distance on ice
The stopping distances above based on dry conditions should be multiplied by 10 for stopping distances on ice.
Stopping distance formula examples
The following stopping distance formulas are based on traveling at a speed of 20 mph.
- Stopping distance in feet
(20) ² ÷ 20 + 20 (thinking distance) = 40 feet - Stopping distance in metres
40 x 0.3 = 12 metres - Stopping distance in rain
80 feet or 24 metres - Stopping distance on ice
400 feet or 120 metres
Stopping distances theory test
The UK theory test involves questions on stopping distances. Although stopping distances are explained above, an easy way for how to remember the overall stopping distances are as follows. When asked for a stopping distance, simply remember the 2 / 2.5 / 3 / 3.5 / 4 / 4.5 from below to work out the overall stopping distance.
| Speed (mph) | Braking distance | Stopping distance |
|---|---|---|
| 20 x | 2 | 40 feet |
| 30 x | 2.5 | 75 feet |
| 40 x | 3 | 120 feet |
| 50 x | 3.5 | 175 feet |
| 60 x | 4 | 240 feet |
| 70 x | 4.5 | 315 feet |
Stopping distances driving test
During a practical driving test, you will not be asked any questions about stopping distances by the examiner at any point. This will have been covered in the theory test. The examiner will however expect that you know the correct stopping distances and to put them into practice during your test.
For example, not driving too close to a vehicle in front and increasing stopping distance if it begins to rain. It can of course be difficult to judge distances in feet whilst driving for anyone. This is why the 2 second rule was developed, to help drivers establish a safe following distance behind another vehicle.
- Read the 2 second rule tutorial complete with diagram to aid understanding. The 2 second rule is multiplied by 2 if it starts to rain.
Braking techniques
To remain safe whilst driving, it’s important to use braking techniques.
- See braking for a guide to progressive braking techniques.