Speed calculator: speed, distance and time in one tool
A speed calculator solves the one equation that ties movement together: speed, distance and time. Give it any two of the three — how far something travelled, how long it took, or how fast it moved — and it works out the missing one, then converts the result into every unit you’re likely to need: kilometres per hour, miles per hour, metres per second, knots and feet per second.
Use it for anything that moves at a roughly constant pace: a car on a motorway, a cyclist’s average over a ride, a ship’s crossing time, a physics problem, or a quick sanity check on a speed figure you’ve seen somewhere. It’s a general speed, distance and time calculator, not a running-specific pace tool — if you’re pacing a run or predicting a race time in min/km, davided.pro’s running pace calculator is built for that.
How to use the calculator
- Choose what to calculate. Pick Speed, Distance or Time from the selector — this decides which two fields you fill in and which one the calculator works out for you.
- Enter the two known values. Type the numbers and pick their units inline — distance in metres, kilometres, miles or nautical miles; time in seconds, minutes or hours; speed in km/h, mph, m/s or knots.
- Read the result. The calculated value appears as the headline number, already converted into every common unit underneath it, so you don’t need a separate converter.
There are no advanced options to configure — this calculator covers the full range of speed, distance and time problems, plus unit conversion, through the fast path alone.
How speed, distance and time are calculated
speed = distance ÷ time (v = d / t)
Rearranged, the same relationship gives you the other two calculations the tool runs:
distance = speed × time (d = v · t) time = distance ÷ speed (t = d / v)
Behind the scenes, every input is first converted into SI base units — metres for distance, seconds for time — using the exact conversion factors defined by NIST (1 mile = 1,609.344 m, 1 nautical mile = 1,852 m exactly). The calculation itself always happens in metres and seconds; only the displayed result is converted into km/h, mph, m/s, knots and ft/s and rounded for display.
Step-by-step example: finding speed
You drive 100 km in 2 hours.
- speed = 100 km ÷ 2 h = 50 km/h.
- In other units, that’s 13.89 m/s, 31.07 mph, 27.00 knots and 45.57 ft/s — the calculator shows all four alongside the headline result.
Finding distance instead
You travel at a steady 80 km/h for 1.5 hours.
- distance = 80 km/h × 1.5 h = 120 km.
- That’s the same as 120,000 m, 74.56 miles, or 64.79 nautical miles.
Finding time instead
You need to cover 150 km at 60 km/h.
- time = 150 km ÷ 60 km/h = 2.5 hours.
- That’s 150 minutes, or exactly 9,000 seconds.
Converting between speed units: km/h, mph, m/s and knots
Every speed result also converts automatically into the units most people need, using exact factors from the NIST Guide to the SI (Special Publication 811) and NOAA’s definition of the nautical mile:
| Unit | Exact conversion to m/s |
|---|---|
| 1 km/h | 1 ÷ 3.6 m/s |
| 1 mph | 0.44704 m/s |
| 1 knot (nautical mile per hour) | 1,852 ÷ 3,600 m/s ≈ 0.5144 m/s |
| 1 ft/s | 0.3048 m/s |
Two worked conversions:
- 1,000 m in 60 s gives 16.6667 m/s, which is exactly 60 km/h and 37.28 mph — a tidy example, since 1,000 m per 60 s happens to land on a round km/h figure.
- 10 nautical miles in 0.5 hours gives exactly 20 knots — equivalent to 37.04 km/h and 10.29 m/s. Knots are the standard speed unit in marine and air navigation, defined as one nautical mile (1,852 m) per hour.
If you only need a one-off conversion — say mph to km/h — pick Speed mode, put your known figure into the speed field with its unit, and any (non-zero) time and distance values work: the result tiles always show the equivalent in every unit at once, so the converted figure is right there next to your input.
Speed vs velocity: what’s the difference
In everyday language “speed” and “velocity” are used interchangeably, but in physics they’re not the same thing. Speed is a scalar — just a magnitude, like “50 km/h.” Velocity is a vector — a magnitude and a direction, like “50 km/h north.” This calculator, like almost every everyday speed tool, computes speed: a plain number, with no direction attached.
There’s a second distinction worth knowing: this tool calculates average speed — total distance divided by total time — not instantaneous speed, which is what a speedometer shows at one exact moment. A trip with an average speed of 50 km/h might include stretches at 0 km/h (stopped at lights) and others at 90 km/h (open motorway); the average smooths all of that into one number. Every result carries a note reminding you it’s an average, assuming constant motion over the whole distance or time entered.