Speed Distance Time Calculator
Know any two of speed, distance and time and this works out the third as you type, in mph or km/h, with the metric and imperial equivalents side by side.
Time = distance divided by speed: driving 30 miles at 70 mph takes 25.7 minutes, and 20 km at 80 km/h takes 15 minutes. Enter any two of speed, distance and time and this calculator finds the third, in mph or km/h, miles or kilometres.
Speeding saves less than you think: driving 60 miles at 80 mph instead of 70 mph saves just 6.4 minutes.
How much time does speeding actually save?
Time saved = distance divided by the legal speed, minus distance divided by the higher speed. The answer is almost always smaller than people expect.
| Journey | At the limit | Speeding | Time saved |
|---|---|---|---|
| 60 miles | 70 mph (51.4 min) | 80 mph (45 min) | 6.4 minutes |
| 100 km | 110 km/h (54.5 min) | 120 km/h (50 min) | 4.5 minutes |
Common trip times at a steady speed:
| Distance | Speed | Time |
|---|---|---|
| 15 miles | 40 mph | 22.5 minutes |
| 30 miles | 70 mph | 25.7 minutes |
| 20 km | 80 km/h | 15 minutes |
| 165 km | 110 km/h | 90 minutes |
What this means for you: over a typical journey, breaking the limit buys minutes at most, against a £100 fine, 3 penalty points and a far higher crash risk. Leave earlier, not faster.
The Speed-Distance-Time Triangle
Three formulas, one relationship. If you know any two, you can calculate the third:
- Speed = Distance / Time, how fast you're going
- Distance = Speed x Time, how far you'll travel
- Time = Distance / Speed, how long the journey takes
The classic memory trick is the SDT triangle: draw a triangle with Distance on top, Speed bottom-left, Time bottom-right. Cover what you want to find. If the remaining two are side by side, multiply them. If one is above the other, divide top by bottom.
These formulas assume constant speed. In reality, your average speed accounts for acceleration, braking, and stops, which is why sat-nav journey times are usually more realistic than dividing distance by speed limit.
Real-World Average Speeds
| Road Type | Speed Limit | Realistic Average | Time for 100 Miles |
|---|---|---|---|
| Motorway (M roads) | 70 mph | 55-65 mph | 1h 32m - 1h 49m |
| Dual carriageway (A roads) | 70 mph | 45-55 mph | 1h 49m - 2h 13m |
| Single carriageway | 60 mph | 35-45 mph | 2h 13m - 2h 51m |
| Urban / city roads | 30 mph | 15-22 mph | 4h 33m - 6h 40m |
| Country lanes | 60 mph | 25-35 mph | 2h 51m - 4h |
What this means for you: Your real average speed is always lower than the speed limit. Traffic, junctions, roundabouts, and speed cameras all reduce it. For planning purposes, assume 55 mph average on motorways and 35 mph on A-roads through towns.
Common Speed Conversions
| mph | km/h | m/s | Context |
|---|---|---|---|
| 20 | 32 | 8.9 | School zones |
| 30 | 48 | 13.4 | Urban speed limit |
| 50 | 80 | 22.4 | Motorway roadworks |
| 60 | 97 | 26.8 | Single carriageway limit |
| 70 | 113 | 31.3 | UK motorway limit |
| 100 | 161 | 44.7 | Fast motorway / unrestricted Autobahn |
| 130 | 209 | 58.1 | Performance car top speed reference |
What this means for you: The quick conversion: multiply mph by 1.6 to get km/h, or divide km/h by 1.6 for mph. For rough mental maths, mph x 1.5 + 10% gets you close enough.
Practical Uses for This Calculator
Planning arrival times
Got 180 miles to drive at an average 50 mph? That's 3 hours 36 minutes. Add 15-20 minutes for fuel and comfort stops on long journeys.
Running and cycling pace
A 5K in 25 minutes means you averaged 12 km/h (7.5 mph). Use the calculator to set target paces for training runs and races.
Speeding fine maths
Doing 80 in a 70 zone saves just 6.4 minutes over 60 miles, but risks a £100 fine and 3 points. The time saving from speeding is almost always trivial.
Delivery and logistics
Multi-stop routes need average speed estimates per leg. Urban legs at 20 mph, motorway at 55 mph, with 5-10 minutes per stop for loading/unloading.
Average Speeds You Can Expect
| Mode of Travel | Average Speed | Planning Notes |
|---|---|---|
| Walking | 3 mph / 5 km/h | Google Maps uses 3.1 mph for walking directions |
| Cycling (city) | 10-12 mph / 16-19 km/h | Include time for traffic lights and junctions |
| Running (casual) | 6 mph / 10 km/h | Roughly a 10-minute mile pace |
| UK motorway | 55-60 mph average | 70 mph limit, but traffic and junctions reduce average |
| UK A-roads | 35-45 mph average | Varies hugely by region and time of day |
| City driving (London) | 7-12 mph | Average London traffic speed is ~11 mph |
The biggest mistake in journey planning: using the speed limit as your average speed. On a 200-mile UK motorway trip, budget for 55 mph average (3h 40m) not 70 mph (2h 50m). Add 15 minutes for fuel and rest stops on trips over 2 hours.
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How to use this tool
Choose which value to calculate: speed, distance, or time
Enter the two known values in your preferred units
Read the answer as you type, with the metric and imperial equivalents beneath it
Common uses
- Estimating journey times for road trips and commutes
- Working out average speed from distance and time
- Planning running, cycling, or walking pace targets
- Calculating delivery route times for logistics
- Converting between mph and km/h for travel abroad
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Frequently Asked Questions
What is the speed distance time formula?
What units are supported?
Can I calculate any of the three?
How do I convert mph to km/h?
What's the average speed for different road types?
Why is my journey time longer than the calculation?
Can I use this for running and cycling?
How much time does speeding actually save?
What is m/s and when do I need it?
How do I calculate average speed for a multi-leg journey?
What speed do delivery drivers average?
Does the calculation work for boats and aircraft?
Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.