The speed triangle
Speed = Distance ÷ Time
Distance = Speed × Time
Time = Distance ÷ Speed
A handy trick: draw a triangle with D on top and S and T underneath. Cover the one you want, and the other two show the formula.
Examples
- Road trip: 150 miles in 2 hours 30 minutes = 60 mph.
- Commute: 18 km at an average of 45 km/h takes 24 minutes.
- Running: 8 mph for 45 minutes covers 6 miles. For pace per mile, use the running pace calculator.
Speed unit conversions
| 1 unit | mph | km/h | m/s |
|---|
| 1 mph | 1 | 1.609 | 0.447 |
| 1 km/h | 0.621 | 1 | 0.278 |
| 1 m/s | 2.237 | 3.6 | 1 |
| 1 knot | 1.151 | 1.852 | 0.514 |
Planning fuel for the trip? The unit converter handles other speed and distance units.
Last reviewed October 2026.
Frequently asked questions
What is the formula for speed?
Speed = distance ÷ time. Rearranged, distance = speed × time and time = distance ÷ speed. A car that travels 150 miles in 2.5 hours averages 60 mph.
How do I convert mph to km/h?
Multiply miles per hour by 1.609344 to get kilometers per hour. 60 mph is about 96.6 km/h. To go the other way, divide by 1.609344.
Is this average speed or instant speed?
It is average speed over the whole trip: total distance divided by total time. Your speedometer shows instant speed, which changes from moment to moment.
Why isn't my average speed the average of two speeds?
If you drive 60 miles at 30 mph and 60 miles back at 60 mph, you spend 2 hours plus 1 hour, so your average is 120 ÷ 3 = 40 mph, not 45. You spend longer at the slower speed, so it counts more.
How do I enter time in hours and minutes?
Use the hours, minutes and seconds boxes. For 1 hour 45 minutes, enter 1 in hours and 45 in minutes. The calculator combines them for you.