DIY Cost Tools
Speed Calculator
SCIENCE CALCULATOR
Speed Calculator
Calculate average speed from distance and elapsed time, with results in miles per hour, kilometers per hour, and meters per second.
How it works
Enter distance and elapsed time, then choose their units. The calculator converts the values to meters and seconds before reporting three common speed units.
Formula
Average speed = distance ÷ elapsed time. 1 m/s = 3.6 km/h and approximately 2.23694 mph.
Worked example
Traveling 120 miles in 2.5 hours gives an average speed of 48 mph, about 77.249 km/h or 21.458 m/s.
Important limits
- Average speed does not show acceleration, stops, or changing speed during the interval.
- Distance traveled is a scalar; velocity also specifies direction.
- Measurement precision limits the meaningful digits in the result.
Frequently asked questions
Is average speed the same as the speedometer reading?
No. A speedometer shows near-instantaneous speed, while this calculator divides total distance by total elapsed time.
Should stops count in elapsed time?
Include them for overall trip speed; exclude them if you want average moving speed.
Sources and review notes
NIST identifies the SI unit of speed as the meter per second; see SI Units – Length. Last reviewed September 29, 2026.