Speed Converter

Convert speed units including kilometers per hour, miles per hour, knots, and meters per second.

Speed Converter

Convert between the common speed units: kilometres per hour, miles per hour, metres per second, and knots. Enter a speed in one unit and the converter returns the equivalents in the others.

Conversion factors

These factors follow directly from the exact definitions of the mile (1,609.344 m) and the nautical mile (1,852 m):

  • 1 m/s = 3.6 km/h (exact, since an hour has 3,600 seconds)
  • 1 mph = 1.609344 km/h (exact)
  • 1 mph = 0.44704 m/s (exact)
  • 1 knot = 1.852 km/h (exact; one nautical mile per hour)
  • 1 knot ≈ 1.15078 mph
  • 1 km/h ≈ 0.621371 mph

To convert km/h to m/s, divide by 3.6; to convert m/s to km/h, multiply by 3.6.

Worked example

Convert a 65 mph US highway speed limit to km/h:

  • 65 × 1.609344 = 104.60736, so 65 mph is about 104.6 km/h.

For a running pace, a treadmill set to 12 km/h in metres per second is 12 / 3.6 = 3.33 m/s, and in mph it is 12 × 0.621371 = 7.456, so about 7.5 mph.

When to use this converter

  • Driving abroad: speed limits are posted in mph in the US and UK but in km/h nearly everywhere else, and a rental car's speedometer may emphasise the wrong scale for the country you are in.
  • Aviation and sailing: wind speeds, airspeeds, and boat speeds are given in knots, which need converting to km/h or mph for intuition.
  • Sports: sprint speeds and cycling data are often quoted in m/s or km/h, while serve and pitch speeds appear in mph in North American coverage.
  • Weather: storm reports mix km/h, mph, and knots depending on the agency issuing them.

Tips for accurate conversions

  • Knots are based on the nautical mile (exactly 1,852 m), not the statute mile, so a 100-knot wind is about 115 mph, not 100 mph.
  • The m/s and km/h relationship is exact and decimal (factor 3.6), which makes it the easiest mental conversion: shift and adjust rather than memorising a rounded factor.
  • Pace and speed are inverses. A pace of 5 min/km equals 12 km/h; converting a pace to another unit is not the same as converting a speed, so convert the speed first and then invert if needed.
  • For quick mental estimates, mph to km/h is roughly "add 60%": 50 mph is about 80 km/h. Use the exact factor 1.609344 when precision matters.
  • Mach numbers are not fixed speeds; they depend on air temperature and altitude, so this converter intentionally sticks to the fixed-definition units above.

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Frequently asked questions

How do I convert km/h to mph?
Multiply km/h by 0.621371, or divide by 1.609344 for full precision. For example, 100 km/h is about 62.14 mph. The factor is exact in reverse: 1 mph equals exactly 1.609344 km/h.
How do I convert m/s to km/h?
Multiply by 3.6, since there are 3,600 seconds in an hour and 1,000 metres in a kilometre. A sprinter running 10 m/s is moving at 36 km/h. To go from km/h to m/s, divide by 3.6.
What is a knot and how fast is it?
A knot is one nautical mile per hour, which is exactly 1.852 km/h or about 1.151 mph. Knots are the standard speed unit in aviation and marine navigation, so a 20-knot wind is about 37 km/h or 23 mph.
Why is a knot faster than a mile per hour?
Because the nautical mile (exactly 1,852 m) is about 15% longer than the statute mile (1,609.344 m). Covering the longer mile in the same hour means a knot represents a higher speed than 1 mph.
How does running pace relate to speed?
Pace is the inverse of speed: a pace of 5 minutes per kilometre equals 60/5 = 12 km/h. To convert a pace to another unit, first convert it to a speed, change units, and invert back if you need a pace again.
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