Speed, Distance & Time Calculator

Speed, distance and time are tied together by a single relationship: Speed = Distance ÷ Time. Give the calculator any two of the three and it returns the third, working in miles per hour, kilometres per hour or metres per second and converting between them automatically. Rearranged, the same relationship gives Distance = Speed × Time and Time = Distance ÷ Speed, which is all the familiar triangle actually says.

The rule that catches people out is that the units have to match. Miles per hour belongs with miles and hours, kilometres per hour with kilometres and hours. Driving 150 miles in 2 hours 30 minutes means dividing 150 by 2.5, which gives 60 mph, and that is also 96.56 km/h or 26.82 m/s. For a journey made of several legs at different speeds, the tool takes total distance over total time, which is the correct average and is not the same as averaging the speeds themselves.

A few conversions are worth carrying in your head. 1 mph is 1.609 km/h, 1 m/s is 3.6 km/h or 2.237 mph, and a knot, being one nautical mile an hour, is 1.852 km/h or 1.151 mph. 60 mph works out at one mile a minute, 88 ft per second or 26.8 m/s, and sits close to 100 km/h, while 100 km/h is 27.78 m/s or 62.1 mph. Further up the scale, Mach 1 at sea level is 1,235 km/h or 767 mph, an airliner cruises at 500-600 mph, Concorde managed 1,354 mph at Mach 2.04, ICE and TGV trains run at 200 mph, the Earth turns at 1,037 mph at the equator, and light travels at 299,792,458 m/s.

UK speed limits set the practical ceiling on any journey. 20 mph has been the default on residential streets in Wales since 2023 and is spreading through English boroughs, 30 mph applies in built-up areas, 40-50 mph appears on signposted A-roads, 60 mph is the national limit on a single carriageway, and 70 mph covers dual carriageways and motorways. Stopping distances grow faster than speed does. The Highway Code puts the total at 23m (75ft) at 30 mph, 73m (240ft) at 60 mph and 96m (315ft) at 70 mph, and every one of those doubles on a wet road. Reaction time alone accounts for 0.7s, which is the thinking behind the two-second gap.

Average speeds in real conditions sit well below the limit. Urban driving averages 12-20 mph and London manages about 12 mph, motorway driving realistically averages 60-65 mph once traffic is counted, and rural A-roads come out at 35-45 mph. London to Manchester, 200 miles, takes roughly 3.5 hours of motorway driving plus breaks, and London to Edinburgh is 8 hours by road against 4.5 hours by train. Under your own power the numbers drop again, with cycling at 12-15 mph around town and 18-22 mph for a club rider, walking at 3 mph strolling and 4 mph briskly, and running at 6 mph recreationally, a 10 min/mile pace, against 10 mph and 6 min/mile for a competitive runner.

The same triangle answers a great many ordinary questions. A train journey uses average speed including stops, so a London to Manchester service averaging 80 mph covers the 200 miles in 200/80, or 2h 30min. Runners invert the sum to get pace, so 10 km in 50 min is a 12 km/h average, which reads as 5:00/km, and the average UK Parkrun finish of 28:30 over 5K works out at 5:42/km. A marathon, 42.195km in 4 hours, is 10.55 km/h. Cyclists trade power for speed, with about 200 watts producing 30 km/h on the flat. The relationship holds for anything that moves, from a car to a projectile to a planet.