Speed, Distance and Time Calculator

How it works

Distance, average speed and time are tied together by one relationship: distance = speed × time. Knowing any two gives the third, so speed = distance ÷ time and time = distance ÷ speed. Average speed here means total distance over total time, which is what a trip computer or a race result reports; it says nothing about how fast you were going at any one moment.

The units can be mixed. Every distance is converted to metres and every speed to metres per hour before the arithmetic, using the exact definitions 1 mile = 1,609.344 m, 1 foot = 0.3048 m and 1 knot = 1,852 m per hour (one international nautical mile per hour). So a distance in miles with a time in hours and minutes can give a speed in km/h or m/s directly.

Time is entered as hours, minutes and seconds and converted to decimal hours (2 h 30 min is 2.5 h). The answer is shown both ways. Minutes and seconds above 59 are accepted and simply added in.

The two-leg mode answers the classic question of averaging speeds. Driving out at 60 mph and back at 40 mph does not average 50 mph: the slower leg takes longer, so the average is total distance over total time, 48 mph for equal legs. The calculator works each leg's time from its distance and speed, adds them, and divides.

Formula

distance = speed × time
speed = distance ÷ time
time = distance ÷ speed
decimal hours = hours + minutes ÷ 60 + seconds ÷ 3600
two legs: average speed = (d₁ + d₂) ÷ (d₁ ÷ v₁ + d₂ ÷ v₂)
1 mi = 1,609.344 m    1 ft = 0.3048 m    1 knot = 1,852 m/h    1 m/s = 3,600 m/h

Example

120 miles in 2 hours is an average speed of 120 ÷ 2 = 60 mph. The same trip measured in km/h is 60 × 1.609344 = 96.5606 km/h.

A marathon is 42.195 km. Run in 2:00:35 (2.0097 hours), that is 42.195 ÷ 2.0097 = 20.9954 km/h.

At 60 mph for 2 hours 30 minutes you cover 60 × 2.5 = 150 miles. Covering 10 km at 5 m/s takes 10,000 ÷ 5 = 2,000 seconds, which is 0:33:20 or 0.5556 hours.

Two legs of 120 miles, out at 60 mph and back at 40 mph: 2 hours out and 3 hours back, 240 miles in 5:00:00, so the average speed is 240 ÷ 5 = 48 mph, not 50.

Assumptions and limitations

• Speed means average speed over the whole distance. Stops, acceleration and traffic are already inside an average measured from the clock; they are not modelled.
• The conversions are the exact international definitions: 1 mile = 1,609.344 m, 1 foot = 0.3048 m, 1 international nautical mile = 1,852 m, so 1 knot = 1,852 m per hour. A statute mile per hour is 1.609344 km/h.
• Minutes and seconds are not limited to 59; 90 minutes counts as 1.5 hours. The h:mm:ss result is rounded to the nearest second, while the decimal hours are not.
• In the two-leg mode both legs share the distance unit and the speed unit chosen above.

Frequently asked questions