Speed Converter
Convert between mph, km/h, m/s and knots.
Results update as you type.
How it works
A speed converter restates a rate of travel in a different unit, moving between metres per second, kilometres per hour, miles per hour, knots and feet per second. It reduces your figure to metres per second, the SI base for speed, then scales out to the unit you want, so a single pivot handles road speeds, wind speeds, running paces and vessel speeds alike. This matters because speed is quoted in different units depending on the setting, and the same journey can look faster or slower purely from the unit. A car's speedometer may read km/h where the limit is posted in mph; a weather forecast gives wind in knots or metres per second; aviation and sailing run on knots entirely. A speed converter reconciles them instantly so comparisons are like for like. The convert-through-metres-per-second method is used because each unit has a fixed ratio to that base — 1 km/h is exactly 1000/3600 m/s, a knot is one nautical mile per hour at 0.514444 m/s — so pivoting through it keeps results exact. Drivers crossing borders, pilots and sailors, meteorologists, athletes checking pace and physics students all use a speed converter whenever a rate arrives in an unfamiliar unit.
Convert to metres per second via known factors, then to the target unit
The input is multiplied by its unit's fixed ratio to metres per second, then divided by the target unit's ratio to land on the answer. This works because every speed unit is a distance unit over a time unit, and both of those reduce to constants against the metre and the second, so their combined ratio to m/s is fixed and pivoting through that one base stays exact.
Source:International System of Units (SI) — NIST
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter value, from and to.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Converted speed updates instantly as you type — no button to press.
Frequently asked questions
How do I convert km/h to mph?
Multiply the km/h figure by about 0.6214 to get mph. So 100 km/h is roughly 62.1 mph, and a 50 km/h urban limit is about 31 mph. To reverse it, multiply mph by 1.60934. The factor is the ratio of a kilometre to a mile, since both speeds share the per-hour time unit, so only the distance part needs converting.
What is a knot?
A knot is one nautical mile per hour, used in aviation and marine navigation because a nautical mile corresponds to one minute of latitude, which makes chart work simpler. One knot is about 1.151 mph or 1.852 km/h. So a ship at 20 knots is doing roughly 23 mph. The unit's name comes from the knotted line sailors once used to gauge a vessel's speed.
How fast is 100 km/h in mph?
About 62.14 mph, which passes through roughly 27.78 metres per second. This is a common motorway or freeway speed. A quick mental shortcut is to multiply km/h by 0.6, giving 60 as a slight underestimate, then nudge up. The converter carries the full 0.62137 factor, so its answer is precise to the decimals displayed rather than the rough estimate.
Why convert through metres per second?
Metres per second is the SI base unit for speed, so every other unit has a fixed, exactly defined ratio to it. Using it as the pivot means the converter needs only one factor per unit rather than a separate rule for each pair, and it keeps results exact. It is also the unit physics equations expect, which is why scientific work quotes speed in m/s.
What is a good running pace in these units?
Running is usually tracked as pace, the time per kilometre or mile, but it converts directly to speed. A brisk 10 km/h equals about 6.2 mph, or a six-minute kilometre. Elite marathon speed is around 20 km/h, roughly 12.4 mph. To turn a speed into pace, divide 60 by the km/h figure to get minutes per kilometre, which many runners find easier to judge.