Stopping Distance Calculator
See your thinking, braking and total stopping distance at any speed, based on the Highway Code's typical stopping distances.
How does the stopping distance calculator work?
Total stopping distance has two parts: thinking distance, which is how far you travel before you start to brake, and braking distance, which is how far the car travels once the brakes are on. The calculator works out thinking distance from your speed and reaction time, and braking distance from your speed, then adjusts braking distance for a wet or icy road.
With the default settings it reproduces the Highway Code's table of typical stopping distances at 20, 30, 40, 50, 60 and 70 mph.
3 worked examples
Example 1 — 30mph, dry road, typical reaction time
This matches the Highway Code's typical figure.
9m (0.67 seconds at 30mph)
Braking distance:14m
Total:23m, about 6 car lengths
Example 2 — 70mph, wet road
The same typical reaction time, in the rain.
21m, unchanged by the weather because it depends on reaction time, not grip
Braking distance (doubled for a wet road):75m × 2 = 150m
Total:about 171m, roughly 43 car lengths, against 96m (24 car lengths) when dry
Example 3 — 30mph, dry road, slower reaction
The same road as Example 1, but a reaction time of 1.5 seconds. This is an illustration of a distracted or tired driver, not a measured figure.
30mph × 1.5 seconds = about 20m
Braking distance:14m, unchanged once braking starts
Total:about 34m, about 11m further than Example 1 before the car has even started to slow down
Example 3 shows how a slower reaction adds distance before braking begins. At 30mph, every extra half-second of delay adds about 6.7m of travel.
Highway Code stopping distances
The Highway Code (Rule 126) includes a table of typical stopping distances, for a car with good brakes and tyres on a dry road:
| Speed | Thinking distance | Braking distance | Total stopping distance |
|---|---|---|---|
| 20 mph | 6m | 6m | 12m (3 car lengths) |
| 30 mph | 9m | 14m | 23m (6 car lengths) |
| 40 mph | 12m | 24m | 36m (9 car lengths) |
| 50 mph | 15m | 38m | 53m (13 car lengths) |
| 60 mph | 18m | 55m | 73m (18 car lengths) |
| 70 mph | 21m | 75m | 96m (24 car lengths) |
Thinking distance grows in step with speed, while braking distance grows much faster: doubling your speed roughly quadruples the braking distance, because the energy to be shed rises with the square of speed.
The table is shown in the Highway Code as a chart, which I could not read directly from GOV.UK's text. The figures here are the widely published ones. Check them against your copy of the Highway Code.
Why distraction and tiredness matter
The typical thinking distance assumes a reaction time of about two-thirds of a second. Anything that slows your reaction lengthens the distance you travel before you brake, and that happens before the car has begun to slow down at all.
Research on phone use has repeatedly found slower reactions. A Transport Research Laboratory study reported in the trade press found hands-free phone use slowed reactions by more than driving at the drink-drive limit did. I haven't found an official figure for how much slower distraction or tiredness makes you, so the calculator lets you enter your own reaction time rather than applying a made-up multiplier.
Holding a phone or similar device while driving carries 6 penalty points and a £200 fine, according to GOV.UK. Drivers within 2 years of passing their test have their licence revoked. You can also be taken to court, with a ban or a fine of up to £1,000 (£2,500 for a lorry or bus). GOV.UK also lists 3 points if you don't have a full view of the road or proper control. Hands-free use is allowed if you never hold the device. See our Penalty Points Calculator.
Why wet and icy roads are so dangerous
The Highway Code says the gap you leave "should be at least doubled on wet roads and up to ten times greater on icy roads". Reduced grip means far more distance is needed to lose the same speed.
The calculator applies a ×2 or ×10 multiplier to braking distance only, because thinking distance depends on reaction time, not on grip. That is the calculator's modelling choice, so the total grows by a little less than the Highway Code's gap guidance. If you are judging a following gap, use the Highway Code's advice and double (or more) the whole gap in the wet.
Tyre condition and stopping distance
Worn tread is generally understood to lengthen braking distances, particularly in the wet, because the tyre clears less water. The calculator doesn't include a tyre multiplier, because the effect varies too much to state a single reliable figure. Check your tread with our Tyre Tread Depth Checker.
What this calculator can't tell you
Your vehicle's actual braking performance
Braking distance varies with weight, brake and tyre condition and the road surface. The calculator uses the Highway Code's typical car figures.
Your personal reaction time
Reaction time varies by person and moment. 0.67 seconds is a typical figure, not a guarantee.
Combined risk factors
Risks stack. A tired driver on a wet road with worn tyres faces a larger increase than any single setting here shows.
Gradients, vehicle types and other speeds
Hills, heavier vehicles and speeds far above 70 mph are not modelled. The braking formula is fitted to the Highway Code's 20–70 mph figures.
Common mistakes
Forgetting thinking distance
Many drivers focus on braking and forget that a large share of the stopping distance is covered before the brakes are applied.
Assuming a safe gap scales in a straight line with speed
Braking distance rises with the square of speed. The total from 30mph to 60mph (23m to 73m) is more than three times as long.
Keeping your usual gap in the rain
The Highway Code says to at least double the gap on wet roads.
Treating hands-free as risk-free
Hands-free use is legal if you don't hold the device, but legal isn't the same as risk-free. You must still be in full control of the vehicle.
Safer following distances
- Use the two-second rule. The Highway Code says to allow at least a two-second gap on high-speed roads, and the gap should be at least doubled on wet roads and up to ten times greater on icy roads
- Pick a fixed point ahead and count the seconds between the vehicle in front passing it and you reaching it
- Don't hold a phone while driving, and avoid any distraction that takes your attention off the road
- Don't drive tired. Take a break rather than pushing on
- Check your tyres regularly, especially before winter or a long wet journey
How we calculate
Thinking distance (m) = speed (mph) × 0.44704 × reaction time (seconds). The Highway Code's thinking distances correspond to a reaction time of 0.67 seconds, which is the default.
Braking distance (m) = 0.0153 × speed² × road multiplier. The formula is fitted to the Highway Code's dry-road braking distances from 20 to 70 mph (6, 14, 24, 38, 55, 75m). The multiplier is ×1 (dry), ×2 (wet) or ×10 (icy or snowy), based on the Highway Code's gap guidance but applied to braking distance only.
Car lengths are the total divided by 4m, which matches the Highway Code table's car-length figures.
Frequently asked questions
What is the stopping distance at 30mph?
The Highway Code's typical figure is 23 metres on a dry road: 9m thinking distance plus 14m braking distance, about 6 car lengths.
How much longer is stopping distance in the wet?
The Highway Code says the gap should be at least doubled on wet roads and up to ten times greater on icy roads. This calculator doubles the braking distance in the wet, because thinking distance isn't affected by grip.
Does using a mobile phone really affect stopping distance?
Phone use has been found to slow reactions, which adds distance before braking starts. Holding a phone while driving is also an offence, with 6 points and a £200 fine, according to GOV.UK.
Why does braking distance increase so much more than thinking distance as speed rises?
Thinking distance rises in step with speed, but braking distance rises with the square of speed because the energy to be shed does. That is why braking distance dominates at higher speeds.
Do worn tyres increase stopping distance?
Generally yes, particularly in wet conditions. The calculator has no tyre setting, so check your tread with our Tyre Tread Depth Checker.
References & data sources
- GOV.UK — The Highway Code: general rules 103 to 158. Rule 126, including the two-second rule and the guidance to double the gap on wet roads and up to ten times on icy roads. The table of typical stopping distances is shown in the Highway Code as a chart.
- GOV.UK — Using a mobile phone when driving: the law. Penalties and the hands-free rules.
- Insurance Times — Research claims hands-free mobiles as bad as drink driving. Trade-press report of a Transport Research Laboratory study of phone use and reaction times. It is an older study and not an official figure.
The calculator's formulas are fitted to the Highway Code's typical figures. The reaction time you enter is your own assumption, and no official multiplier exists for tiredness or distraction.
Prakash
Prakash is the founder and editor of UK Driving Tools. He maintains the site's calculators and guides and checks the rates and rules they use against official UK sources, such as GOV.UK, the DVLA, HMRC and Transport for London, before publishing.
Pages are drafted with the help of AI tools and then checked by the editor. He isn't a lawyer, accountant or UK-qualified adviser, so every page lists its sources and states what its calculator can't tell you. Nothing on this site is legal or financial advice.
Pages on UK Driving Tools are drafted with the help of AI tools. Before publishing, the figures and rules on each page are checked against the official source named on the page, and calculator examples are tested against the working formula. Pages are updated when rates or rules change. Our Editorial Policy explains the full process, including how to report a mistake.
Spotted a mistake or an out-of-date rate? Let us know and we'll check it against the official source.