Speed Distance Time Calculator
Pick what you want to find — speed, distance, or time — enter the other two, and get an average-speed answer. Switch between kilometres and miles whenever you need.
Calculate
Calculate
Measurements convert when you switch units
Result
The formula
Average speed, distance, and time form a closed triangle: speed = distance ÷ time, distance = speed × time, and time = distance ÷ speed. Use consistent units (km with km/h, or miles with mph). Time is entered as hours, minutes, and seconds and converted to decimal hours internally.
Worked example
- Find time for 120 km at 80 km/h
- t = 120 ÷ 80 = 1.5 hours
- 1.5 h = 1h 30m 0s
Result: 1h 30m 0s
How speed, distance, and time relate
This tool uses constant average speed over the whole trip — the same relation taught in school physics and used for rough ETAs on maps.
The SDT triangle
Cover any two of speed, distance, and time and the third follows. Solving for speed answers “how fast on average?”; solving for distance answers “how far at this pace?”; solving for time answers “how long will it take?”
Units
Metric mode treats distance as kilometres and speed as km/h. Imperial mode uses miles and mph. Do not mix systems in one calculation — the unit toggle keeps labels and conversions aligned.
Time inputs
Hours, minutes, and seconds are added into one duration. When the result is a travel time, we round to the nearest second and show h/m/s. Very short trips may display only minutes and seconds.
Average vs instantaneous speed
The result is average speed over the interval you entered. Stops, traffic, and hills change how long a real trip takes even when the odometer distance is fixed.
What we do not model
No acceleration, speed limits by segment, rest stops, or GPS path length vs road length. For running pace (min/km), use the pace calculator; for fuel cost on a trip, use trip fuel cost.
Interesting facts
Older than the car
The distance = rate × time idea appears in early algebra texts long before motorcars — merchants and sailors used the same proportion with leagues and knots.
km/h vs m/s
SI base units use metres and seconds, so 1 m/s = 3.6 km/h. Road signs and this calculator stay in km/h or mph because that is how people plan trips.
Average hides variation
A 100 km trip that takes 2 hours averages 50 km/h even if part of the route was 100 km/h motorway and part was stop-and-go city traffic.
Light as a benchmark
In vacuum, light travels about 299,792 km/s — useful for science demos, not road ETAs. Everyday SDT problems stay in human travel speeds.
Why maps pad ETAs
Navigation apps add traffic models and typical pause time on top of pure d ÷ v. This calculator stays transparent: only the numbers you type.
Frequently asked questions
Divide distance by time in hours. Example: 150 km in 2 hours → 75 km/h. Choose “Find speed” in this calculator and enter distance plus hours/minutes/seconds.
Divide distance by average speed. Example: 240 miles at 60 mph → 4 hours. Use “Find time” with matching units (miles with mph, or km with km/h).
Multiply speed by time in hours. Example: 90 km/h for 1 hour 20 minutes (1.333… h) → about 120 km.
The three forms are v = d/t, d = v×t, and t = d/v. They are rearrangements of the same average-speed definition.
Match the unit system to your road signs and odometer. Use the metric/imperial toggle so distance and speed stay consistent.
Related but different: pace is usually minutes per kilometre or mile. This tool reports clock time and average speed in km/h or mph — better for driving, cycling, or general word problems.
Apps forecast traffic, turns, and typical speed profiles. This calculator assumes a single average speed for the whole distance you enter.
Yes — leave hours at 0 and put minutes (and optional seconds) in their fields. 45 minutes is 0.75 hours when solving for speed or distance.
References
- NIST Guide to the SI Authoritative guidance on SI units for length and time.
- OpenStax College Physics — Uniform Motion Clear treatment of average speed as distance over time.
- BIPM SI Brochure Definitions of the metre and the second.