Speed Distance Time
Enter any two, get the third โ km/h, mph, m/s and knots handled.
About this calculator
The classic triangle: speed = distance รท time, and the other two by rearrangement. Pick what you're solving for, enter the other two in whatever units suit โ kilometres against mph against knots all mix freely โ and the answer arrives with its conversions.
Averages, and why journeys lie
The number this calculator gives is average speed, and averages hide texture: a 100 km trip at "80 km/h" that includes one fuel stop and two towns was mostly driven at 95. Planning rule from the road: expect door-to-door averages 10โ20% below cruising speed. The trap question every physics teacher loves: drive somewhere at 30 and return at 60 โ your average is 40, not 45, because you spent twice as long at the slow speed (averages weight by TIME, not distance). A knot, for the curious, is one nautical mile per hour โ 1.852 km/h โ the sea and sky's unit because a nautical mile is a minute of latitude. Runners wanting min/km pace and splits have their own calculator; unit conversion alone lives in the unit converter.
Frequently asked questions
How do I calculate average speed?
Total distance รท total time โ 300 km in 3.5 hours is 85.7 km/h. Note it weights by time: half an hour at 30 plus half at 90 averages 60, but equal DISTANCES at 30 and 90 average only 45.
How long will my journey take?
Distance รท speed: 240 km at 80 km/h is 3 hours. Add 10-20% for real-world stops and towns โ cruising speed isn't journey speed.
What is a knot?
One nautical mile (1.852 km) per hour. Ships and aircraft use it because the nautical mile is one minute of latitude, which makes chart navigation arithmetic clean.
How do I convert m/s to km/h?
Multiply by 3.6 (3,600 seconds per hour รท 1,000 m per km). 10 m/s = 36 km/h โ the calculator mixes units for you.