Speed Converter
Convert between km/h, mph, m/s, knots, and Mach number instantly.
Did this tool work for you?
How to use this calculator
- 1
Enter the speed value you want to convert.
- 2
Select the unit you are converting from (e.g. km/h).
- 3
Select the unit you want the result in (e.g. mph).
- 4
The result appears instantly.
Frequently asked questions
How do I change km/h to mph?
Multiply km/h by 0.6213711922, which comes from 1 mile = 1.609344 km exactly. So 100 km/h is 62.13711922 mph and 120 km/h is 74.56454307 mph. In the other direction, multiply mph by 1.609344, giving 70 mph = 112.65408 km/h.
How do I change m/s to km/h?
Multiply by 3.6, exactly, because an hour has 3,600 seconds and a kilometre has 1,000 metres. Therefore 10 m/s is 36 km/h and 1 m/s is 3.6 km/h. Dividing km/h by 3.6 gives m/s: 120 km/h is 33.33333333 m/s.
What is a knot?
One knot is one nautical mile per hour, so 1.852 km/h, 0.51444444 m/s or 1.150779448 mph. It is the standard unit in shipping and aviation. Writing “knots per hour” is incorrect, because the hour is already part of the unit.
What speed does Mach 1 mean in this tool?
The converter fixes Mach 1 at 340.29 m/s, the speed of sound in air at sea level under standard conditions. That is 1,225.044 km/h or 761.2070508 mph. Real sound speed depends on air temperature, so at altitude or in hot weather the true Mach 1 differs and the answer is only an approximation.
Are the miles in mph statute or nautical?
Statute miles of 1,609.344 m. A mile per hour is therefore 0.44704 m/s, exactly, and 60 mph is exactly 88 ft/s. Nautical miles per hour are knots, a separate entry.
Can it convert pace, such as minutes per kilometre?
No. Pace is the reciprocal of speed and the tool does not include it. It also does not cover vertical speed, rotational speed in rpm or relativistic speeds. It handles linear speed in the six listed units.
How precise is the result?
The factors are exact for km/h, mph, knots and ft/s, and the result shows up to ten significant digits. A speedometer or radar reading is accurate to far fewer digits, so round the answer to something sensible, such as one decimal.
Speed units: km/h, mph, m/s, knots and Mach
Exact relationships between speed units
Each speed unit is a distance over a time. A metre per second is exactly 3.6 km/h. A mile per hour is 1,609.344 m over 3,600 s, which is 0.44704 m/s exactly. A knot is one nautical mile of 1,852 m per hour, 0.51444444 m/s or 1.852 km/h. A foot per second is 0.3048 m/s, or 1.09728 km/h. The converter works from these definitions, passing every conversion through metres per second. Because every unit is an exact ratio to the metre per second except Mach, you can chain conversions without accumulating rounding error: km/h to mph and back returns the original figure.
Reference values taken from the converter
Each row begins with one unit and shows the same speed in four others, copied from the tool’s output.
| From | km/h | mph | m/s | Knots |
|---|---|---|---|---|
| 1 km/h | 1 | 0.62137119 | 0.27777778 | 0.5399568 |
| 1 mph | 1.609344 | 1 | 0.44704 | 0.86897624 |
| 1 knot | 1.852 | 1.150779448 | 0.51444444 | 1 |
| 1 m/s | 3.6 | 2.236936292 | 1 | 1.943844492 |
| 1 ft/s | 1.09728 | 0.68181818 | 0.3048 | 0.5924838 |
Worked examples: roads and boats
A limit of 100 km/h is 62.13711922 mph, and a limit of 70 mph is 112.65408 km/h. A car travelling at 120 km/h covers 33.33333333 m per second. A boat doing 30 knots goes 55.56 km/h, or 34.52338344 mph. Finally, 60 mph is exactly 88 ft/s, a handy check for anyone working with imperial speeds. Travel examples help sense the scale: a 50 km/h urban limit is 13.88888889 m/s in the tool’s arithmetic, and a walker at 1.4 m/s moves at 5.04 km/h.
Mach is not a fixed speed
The Mach entry multiplies by 340.29 m/s, the speed of sound at sea level in standard air. One Mach is then 1,225.044 km/h and 761.2070508 mph. Sound travels more slowly in cold air, so Mach 1 at cruising altitude is a lower number of km/h than at sea level. For serious aviation or ballistic work, use the local speed of sound instead of this default.
What the converter leaves out
Pace, vertical speed, rpm and acceleration are separate quantities, and the tool only handles straight-line speed. For journey planning, divide a distance by a speed in matching units, or use a dedicated distance, speed and time calculator. The output precision is about ten digits, so round to match your source.
Learn more from an authoritative source:
NISTTime Unit Converter
Convert between seconds, minutes, hours, days, weeks, months, and years instantly.
Data Storage Converter
Convert between bits, bytes, kilobytes, megabytes, gigabytes, terabytes, and petabytes.
Pressure Converter
Convert between pascals, bar, PSI, atmospheres, torr, and other pressure units.
Energy Converter
Convert between joules, kilocalories, kilowatt-hours, BTU, electronvolts, and other energy units.
Power Converter
Convert between watts, kilowatts, horsepower, BTU/hour, and other power units.
Number Base Converter
Convert numbers between decimal, binary, hexadecimal, and octal instantly.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →