Speed is the rate of covering distance — the most basic relationship in motion.
Speed = Distance ÷ Time
Where
| Distance | How far you traveled |
| Time | How long it took |
Worked example
Covering 120 miles in 2 hours gives 120 ÷ 2 = 60 mph.
Vehicle road speed also depends on tire size, transmission gear, and axle ratio — change a tire diameter and the speedometer reads differently.
FAQ
Does this formula account for acceleration or just constant speed? It calculates average speed over a distance and time, which works for constant speed but represents an average value if speed varied throughout the trip, not the instantaneous speed at any single moment.
What units should I use to avoid mistakes? Keep distance and time units consistent with your desired speed unit, for example miles and hours for mph, and convert before calculating if your raw data uses different units, like minutes instead of hours.
See the Speedometer Error calculator in the automotive calculators.