Speed Calculator
Solve v = d / t for speed, distance or time from the other two. Work in miles, mph and hours or in kilometers, km/h and hours.
How to use the Speed Calculator
- Enter your numbers in the Speed Calculator above.
- Press the Calculate button to see the result.
- To try other numbers, change any value and press the button again.
The speed equation
v = d / t · · · d = v × t · · · t = d / v
v is speed, d is distance, t is time. All three use the same system: miles, mph and hours, or kilometers, km/h and hours. The US / Imperial and Metric switch picks which units you type and read. It does not convert between them, so use the FAQ below to change km/h into mph. Time is always in hours, so enter 30 minutes as 0.5.
Worked example
You drive 300 km in 4 hours. Pick Metric, solve for speed and enter 300 and 4: the average speed is 300 / 4 = 75 km/h. To cover 200 miles at 60 mph, solve for time: 200 / 60 = 3.3333 hours, which the calculator also shows as 3 h 20 min.
Frequently asked questions
What's average vs. instantaneous speed?
Average speed = total distance / total time, even if you stopped along the way. Instantaneous speed = speed at a specific moment (what your speedometer shows).
How do I convert km/h to mph?
The NIST Guide to the SI, Appendix B.9, defines one mile as exactly 1.609344 km. So divide km/h by 1.609344, or multiply by about 0.621371. 100 km/h is about 62.14 mph, and 60 mph is 60 × 1.609344 = 96.56 km/h.
What about acceleration?
Acceleration is the change in speed over time: a = Δv / Δt, measured in m/s² or mph/s. 0–60 mph times measure acceleration; lower time = higher acceleration.