Speed Calculator

Speed, distance, and time are three quantities linked by a single relationship: speed equals distance divided by time. If you know any two of them, the third is just a calculation away. This calculator lets you pick which quantity you want to find, enter the other two, and get an instant answer with unit conversions included. The formula is taught in every physics and maths class because it applies everywhere from road trips and running pace to aviation and particle physics. It assumes a constant (average) speed over the entire interval. If speed varies, the result is still the correct average speed for that distance and time. Distance and time inputs default to kilometres and hours, which gives speed in km/h. The result also shows the equivalent in miles per hour for quick comparison with speed limits or stats from different countries.

• Road trip planning: Enter the distance to your destination and your expected average speed to find out how many hours the drive will take. Account for stops by adding extra time separately.
• Running and cycling pace: Enter the distance of a race and your finishing time to calculate average speed in km/h or mph. Useful for comparing performances across different course lengths.
• Estimating arrival time: If you know how far you are from a destination and the speed limit, solve for time to get a minimum travel duration before adding buffer for traffic or stops.
• Physics homework: The v = d/t formula is one of the first equations in kinematics. Use this calculator to check worked problems or verify that your rearranged formula gives the same answer.

• Mixing up units: Speed in km/h combined with distance in miles gives a nonsense answer. Always use consistent units. Convert everything to the same system before entering values.
• Entering time in minutes instead of hours: The default time unit is hours. If your travel time is 90 minutes, enter 1.5 hours, not 90. Entering 90 hours gives a speed 60 times too slow.
• Confusing average speed with top speed: This formula gives average speed over an interval. A car that averaged 80 km/h may have reached 120 km/h on the motorway and stopped at traffic lights in between.
• Forgetting that zero speed is undefined for time calculation: Dividing distance by zero speed is mathematically undefined and physically means you never arrive. The calculator catches this and returns an error.

1. 1Select which quantity you want to calculate: speed, distance, or time.
2. 2Enter the two known values in the fields shown.
3. 3For speed: the calculator divides distance by time and converts the result to mph.
4. 4For distance: it multiplies speed by time and converts to miles and metres.
5. 5For time: it divides distance by speed and converts to minutes and seconds.
6. 6All inputs must be greater than zero; the calculator returns an error otherwise.

• Use decimal hours, not HH:MM: For a 2-hour 45-minute journey, enter 2.75 hours (2 + 45/60). The calculator does not parse time in HH:MM format for this input.
• Convert km/h to m/s by dividing by 3.6: Physics problems often require speed in metres per second. Divide any km/h result by 3.6. For example, 90 km/h = 25 m/s.
• Check speed limits in the correct unit: The UK and US use mph for speed limits. Most of the rest of the world uses km/h. The calculator always shows both so you can cross-check without mental arithmetic.
• Chain calculations for multi-leg journeys: For a trip with different speeds in each leg, calculate time for each leg separately, then add the times together. The average speed over the whole trip is total distance divided by total time.