What the Speed Distance Time Calculator does
This calculator solves speed, distance or time when you know the other two, in whichever units you have - kilometres or miles, km/h, mph, m/s, knots, or a running pace in minutes per kilometre or mile - and shows the working with the formula. It also finds the true average speed over several legs of a journey, which is not the average of the leg speeds.
Times can be typed the way you would say them: 2:30, 1:05:30, 2h 30m, 90 min or 2.5 hours. Every answer is converted into all the other units, so you can read off a speed in mph and knots or a pace per mile at the same time. The arithmetic runs in your browser; nothing is sent anywhere.
How to use it
- Choose what you want to find: speed, distance or time. The calculator hides the box for that one and asks for the other two.
- Type the values and pick their units. For a pace, choose min/km or min/mile and type minutes and seconds, such as 5:30.
- Read the answer at the top, the two-line working underneath and the same speed in every unit in the table. Change "Show speed in" to have the headline in mph, knots or pace.
- For a journey in stages, choose "Average speed over legs" and give each leg a distance and either its speed or the time it took. The result is total distance divided by total time, with the misleading simple average shown beside it.
- Copy the answer or download the figures as CSV.
Reading the results
The answer is an average. A drive of 150 km in two and a half hours averages 60 km/h whatever the speedometer showed along the way, so a time worked out from a cruising speed will be optimistic if the trip includes towns, traffic or stops.
In the multi-leg result, the tile marked "not the average speed" is the simple mean of the leg speeds. It is only right when every leg took the same time; when the legs are the same distance, the true average is the harmonic mean and is always lower.
Worked example: a drive, a marathon and a boat trip
Speed: 150 km in 2 hours 30 minutes is 150 ÷ 2.5 = 60 km/h, which is 60 ÷ 1.609344 = 37.28 mph and a pace of 1:00 per kilometre.
Time: a marathon is 42.195 km. At 5:30 per kilometre (330 seconds) it takes 42.195 × 330 = 13,924.35 seconds, which is 3 hours 52 minutes 4 seconds.
Distance: a boat at 15 knots for 3 hours 20 minutes covers 15 × 3.3333 = 50 nautical miles, which is 92.6 km.
Average over legs: 60 km at 30 km/h takes 2 hours and 60 km at 60 km/h takes 1 hour, so 120 km takes 3 hours - an average of 40 km/h. Averaging 30 and 60 gives 45, which would be wrong.
Formulas and scoring rules
- Speed
speed = distance ÷ time- Distance
distance = speed × time- Time
time = distance ÷ speed- Pace
pace (min per km) = 60 ÷ speed (km/h)Pace is the inverse of speed; 12 km/h is 5:00 per km.- Average speed over legs
average = (d1 + d2 + ...) ÷ (t1 + t2 + ...)For n legs of equal distance this equals the harmonic mean n ÷ (1/v1 + 1/v2 + ...).- Unit definitions
1 mi = 1.609344 km; 1 nmi = 1.852 km; 1 knot = 1.852 km/h; 1 mph = 0.44704 m/s; 1 m/s = 3.6 km/hExact definitions; results are rounded only for display.
Why the average speed is not the average of the speeds
Speed is distance per unit time, so an average speed has to be weighted by time. On a trip with a slow leg and a fast leg of the same length, you spend longer on the slow one - in the example, two hours at 30 km/h against one hour at 60 km/h. Two thirds of the time at 30 and one third at 60 averages 40 km/h. The simple mean of 45 treats both legs as if they took equally long.
This is the classic "how fast must I drive back to average 60?" puzzle: if you drove there at 30 km/h, no speed on the return leg of the same length can bring the round trip up to 60, because you have already used the whole time budget on the way out.
Limitations: what the result does not prove
- It works with constant average speeds. Acceleration, braking and changes of speed within a leg need the physics of motion, not this triangle.
- Journey times for driving, cycling or sailing are best-case estimates. Stops, traffic, gradients, wind and current are not included.
- Distances are what you type. Straight-line distances on a map are shorter than the road or route you will actually travel.
- Knots are nautical miles per hour and are used at sea and in aviation. A nautical mile (1,852 m) is longer than a statute mile (1,609.344 m).
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- NIST SP 811 - Guide for the Use of the International System of Units - checked 19 Sep 2026
- BIPM - The International System of Units (SI Brochure), non-SI units accepted for use
- OpenStax College Physics - Speed, velocity and average speed
Frequently asked questions
What is the formula for speed, distance and time?
Speed equals distance divided by time; distance equals speed multiplied by time; time equals distance divided by speed. Keep the units consistent - kilometres with hours give km/h - or let the calculator do the conversions for you.
How do I work out travel time from distance and speed?
Divide the distance by the speed. 225 km at 90 km/h is 2.5 hours, or 2 hours 30 minutes. Choose "Time", enter the distance and speed, and the answer appears in hours, minutes and seconds.
How do I calculate average speed for a journey with stops or several parts?
Add up all the distances and divide by the total time, including the time you were stopped if you want the overall average. Use the legs mode to enter each part with its own speed or time.
How many km/h is one knot?
Exactly 1.852 km/h, because a knot is one nautical mile per hour and a nautical mile is defined as 1,852 metres. In miles per hour a knot is about 1.151 mph.
How do I convert a running pace to speed?
Divide 60 by the pace in minutes. A pace of 5:00 per kilometre is 60 ÷ 5 = 12 km/h; 8:00 per mile is 7.5 mph. Choose a pace unit for the speed and the table shows every equivalent.
If I drive at 30 km/h one way and 60 km/h back, what is my average speed?
40 km/h, not 45. The slower leg takes twice as long, so it counts twice as much. For two legs of equal length the average is 2 ÷ (1/30 + 1/60), the harmonic mean of the two speeds.
Last reviewed by the A2Z.Tools team against the sources listed above.
