Most learners try to memorise stopping distances as random numbers and fail their theory test. The actual method that works involves understanding the pattern behind the figures and connecting them to real driving conditions. With only 46% of learners passing their theory test, knowing how to tackle stopping distance questions could make the difference between passing and failing.
At 30 mph, your total stopping distance is 23 metres in perfect conditions. At 70 mph on a motorway, that figure jumps to 96 metres – longer than a football pitch. These aren’t just exam numbers. Inappropriate stopping distances contribute to over 40% of crashes on UK roads, yet only one in three drivers can correctly estimate safe stopping distances. Understanding how these distances work will help you pass your test and stay safe on British roads.
The two-part formula behind every stopping distance
Your total stopping distance splits into two distinct parts: thinking distance and braking distance. Thinking distance covers the ground you travel during the reaction time before your foot even touches the brake pedal. Braking distance measures how far your car continues after you apply the brakes until it stops completely.
The pattern becomes simple once you spot it. The thinking distance at 20 mph is 6 metres, at 30 mph is 9 metres, at 40 mph is 12 metres. Notice that each 10 mph adds 3 metres. Braking distance follows a different rule – it increases as the square of your speed. Double your speed, and your braking distance multiplies by four.
Visualizing the exponential growth in stopping distances
| Speed | Thinking Distance | Braking Distance | Total Stopping Distance |
| 20 mph | 6 metres | 6 metres | 12 metres |
| 30 mph | 9 metres | 14 metres | 23 metres |
| 40 mph | 12 metres | 24 metres | 36 metres |
| 50 mph | 15 metres | 38 metres | 53 metres |
| 60 mph | 18 metres | 55 metres | 73 metres |
| 70 mph | 21 metres | 75 metres | 96 metres |
The chart below illustrates how thinking distance (blue) increases steadily while braking distance (red) grows exponentially with speed. Notice how at 20 mph, both components are equal at 6 metres each, totalling just 12 metres. By 70 mph, the braking distance alone reaches 75 metres – more than six times longer than the entire stopping distance at 20 mph. This visual representation makes it clear why speed limits matter so much for road safety.
When the weather changes everything
Wet roads can double your braking distance or worse. Rain creates a film between your tyres and the road surface, reducing grip significantly. Ice multiplies stopping distances by up to ten times compared to dry conditions – what takes 23 metres at 30 mph in summer could require over 200 metres on icy winter roads.
The Highway Code recommends leaving at least a two-second gap between you and the vehicle ahead in good conditions, extending this to four seconds in wet weather and ten times more on ice. However, only 26% of drivers surveyed knew that the correct stopping distance at 70 mph is 24 car lengths, suggesting many drivers underestimate the space needed.
Why your brake system determines real-world stopping power
Theory test numbers assume your brakes work properly. In reality, worn brake pads can add several metres to your stopping distance or cause complete brake failure. According to autodoc.co.uk, the brake discs typically last between 50,000 and 80,000 miles when properly maintained, though city driving with frequent stops wears them considerably faster than motorway cruising.
Brake pad thickness should be kept above 3mm for safe braking, with most new pads starting at 10 to 12mm thick. Most manufacturers recommend inspection every 12,000 miles to catch wear before it becomes dangerous.
Worn brake pads or damaged brake discs are usually the most common cause of squealing, grinding, or scraping noises when braking. Squealing typically means your brake pads have reached their wear indicators – small metal tabs designed to alert you when replacement is due. Grinding or scraping sounds are more serious and may be telling you that the brake pads have worn completely through, and metal is rubbing against metal. Check your car brake pads through the wheel spokes – if you can’t see any pad material or notice deep grooves in the discs, stop driving immediately. You can also listen while someone else brakes slowly in a safe area.
These warning signs shouldn’t be ignored. The progression from squealing to grinding represents the difference between a routine maintenance appointment and a potential brake failure that could add dangerous extra metres to your stopping distance.
Passing your test and driving safely
Remember the basic pattern: thinking distance increases steadily with speed at 3 metres per 10 mph, while braking distance increases exponentially. The 20 mph figures are both 6 metres, making that speed easy to remember as your starting point.
On the actual test, questions might ask you to calculate total stopping distance at a given speed, identify thinking or braking distance separately, or explain how conditions affect these figures. Understanding the logic behind the numbers beats pure memorisation every time.
Your theory test score matters less than genuinely understanding what these distances mean for your safety and that of everyone sharing the road with you.
The article is based on data from the Highway Code, official DVSA statistics on theory test results (gov.uk), Driving Test Success data on theory test pass rates for 2024, AUTODOC technical recommendations for brake system maintenance, and statistics on road accidents in the UK.
FAQ
Q: What’s the easiest way to remember stopping distances for the theory test? A: Start with 20 mph, where both thinking and braking distances equal 6 metres (12 metres total). For thinking distance, add 3 metres for every 10 mph increase. For braking distance, remember it grows exponentially – doubling your speed quadruples your braking distance.
Q: How do I know when my brake pads need replacing? A: Listen for squealing noises when braking, which indicate your pads have reached their wear indicators. If you hear grinding or scraping sounds, stop driving immediately – this means the pads have worn through completely. Visually check through the wheel spokes that the pad material is visible and the brake discs don’t have deep grooves. Keep pad thickness above 3mm and inspect every 12,000 miles.
Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.