Case 1
- How fast are you going?
- 50km/h
- Reaction time
- 1s
- Friction coefficient (μ)
- 0.8
- Gravity (g)
- 9.81m/s²
26.18m
Open with these valuesStopping Distance Calculator
97.85m
Result: 97.85 mThe total is the reaction distance plus the braking distance, not the braking distance alone. At 100 km/h with a 1.5 s reaction and dry asphalt you travel 41.67 m before the brakes bite and 56.18 m while they work — 97.85 m in all. Doubling the speed more than doubles it, because the braking part goes with v².
Worked examples
Case 2
- How fast are you going?
- 100km/h
- Reaction time
- 1.5s
- Friction coefficient (μ)
- 0.7
- Gravity (g)
- 9.81m/s²
97.85m
Open with these valuesCase 3
- How fast are you going?
- 120km/h
- Reaction time
- 2s
- Friction coefficient (μ)
- 0.5
- Gravity (g)
- 9.81m/s²
179.93m
Open with these valuesHow it's calculated
d = v × t + v² ÷ (2 × μ × g), with v = km/h ÷ 3.6
- StepEnter the speed in km/h — it is converted to m/s internally.
- StepEnter your reaction time; 1.5 s is the standard baseline.
- StepPick the grip: 0.7 dry asphalt, 0.4 wet, 0.1 ice.
- ResultRead the total distance from spotting the hazard to standing still.
Reference table
| Speed, reaction, μ, g | Road | Total stopping distance (m) |
|---|---|---|
| 30, 1.5, 0.7, 9.81 | Dry, in town | 17.56 |
| 50, 1, 0.8, 9.81 | Dry, sharp tyres | 26.18 |
| 80, 1, 0.6, 9.81 | Damp country road | 64.17 |
| 100, 1.5, 0.7, 9.81 | Dry motorway | 97.85 |
| 120, 2, 0.5, 9.81 | Wet, tired driver | 179.93 |
Questions
How do I calculate total stopping distance?
Add the reaction distance to the braking distance. Convert the speed to m/s (km/h ÷ 3.6), then reaction distance = v × t and braking distance = v² / (2 × μ × g). At 100 km/h with a 1.5 s reaction time on dry asphalt (μ = 0.7), that is 41.67 m + 56.18 m = 97.85 m.
What is the difference between reaction distance and braking distance?
Reaction distance is how far you travel between spotting a hazard and pressing the brake — it depends only on your speed and reaction time, not on the brakes or the road. Braking distance is how far you travel once the brakes are slowing you down, and it depends on speed, grip, and gravity. This calculator returns the two added together.
Why does doubling my speed more than double the stopping distance?
Because speed enters the braking term squared: braking distance = v² / (2 × μ × g). Doubling your speed quadruples the braking distance while the reaction distance only doubles. At higher speeds the braking part dominates, so a small increase in speed has an outsized effect.
What friction coefficient should I use?
Use roughly 0.7 for dry asphalt, 0.4 for wet asphalt, and 0.1 for ice or packed snow. The coefficient μ describes how much grip the tyres have. Going from dry to wet roughly doubles the braking part of the stop while leaving the reaction distance unchanged.
Is the calculated stopping distance exact?
It is a physics-based estimate, not a guarantee: the model assumes constant deceleration and one representative grip value. Real stops vary with ABS, brake fade, gradients, tyre wear, load, and your actual reaction time. Treat the number as a best-case ballpark and keep a generous margin on the road.
Sources and last check
Information, not professional advice.