Speed unit reference table
Exact kilometers-per-hour equivalents for every unit supported by this converter.
| Unit | Symbol | km/h equivalent |
|---|---|---|
| Kilometer per hour | km/h | 1 km/h |
| Mile per hour | mph | 1.609344 km/h |
| Meter per second | m/s | 3.6 km/h |
| Knot | kn | 1.852 km/h |
- The m/s ↔ km/h factor (3.6) is exact, derived directly from the definitions of the kilometer and the hour — not a rounded approximation.
- A knot (nautical mile per hour) is about 15% faster than a mile per hour, because the nautical mile (1,852 m) is longer than the statute mile (1,609.344 m).
- This calculator converts speed as a scalar magnitude; it does not account for direction (velocity) or for reference frame (for example, airspeed versus groundspeed).
How are speed units defined?
Speed is distance traveled per unit of time, so every speed unit derives directly from a length unit and a time unit that are each already exactly defined. The meter per second (m/s) is the SI coherent unit of speed; kilometers per hour and miles per hour scale it using the exactly defined kilometer, mile and hour, so 1 m/s equals exactly 3.6 km/h — not an approximation, but a direct consequence of 1 km = 1,000 m and 1 hour = 3,600 seconds.
The knot is a unit of speed equal to one nautical mile per hour, used in aviation, maritime navigation and meteorology. The international nautical mile was fixed at exactly 1,852 meters by international agreement at the 1929 Extraordinary International Hydrographic Conference in Monaco, and this figure was subsequently adopted by the world's major maritime and aviation authorities. Because 1 nautical mile (1,852 m) differs from 1 statute mile (1,609.344 m), a knot and a mile per hour are not the same speed — 1 knot equals about 1.151 mph.
How to use this speed converter
- Enter the speed value you want to convert.
- Select the unit that value is currently in — km/h, mph, m/s or knots.
- Read the converted results across the other three units, shown at once.
- When working with aviation, marine or weather data reported in knots, remember they represent nautical miles per hour, not statute miles per hour.
The formula behind speed conversion
Every input value is first converted to kilometers per hour using its exact factor, then re-expressed in each other unit by dividing by that unit's own km/h-equivalent. All factors below are exact, derived directly from the defined meter, mile and international nautical mile.
Common mistakes
- Confusing knots (nautical miles per hour, used in aviation and at sea) with statute mph — a wind reported at 20 knots is about 23 mph, not 20 mph.
- Treating the m/s-to-km/h factor of 3.6 as a rough rule of thumb rather than the exact value it actually is.
- Rounding the mph-to-km/h factor too aggressively — using 1.6 instead of the exact 1.609344 introduces meaningful error over long distances.
- Using speed and velocity interchangeably — speed is a magnitude only; direction of travel is not part of any of the units this converter handles.
Frequently asked questions
How do you convert km/h to mph?
Divide the kilometers-per-hour value by 1.609344, the exact number of kilometers in a statute mile. For example, 100 km/h converts to 100 ÷ 1.609344 ≈ 62.14 mph.
What is a knot in mph?
One knot (one nautical mile per hour) equals approximately 1.15078 mph, because the international nautical mile (1,852 m, fixed in 1929) is longer than the statute mile (1,609.344 m) used to define mph. Knots are the standard speed unit in aviation, marine navigation and meteorology.
Why is 1 m/s exactly 3.6 km/h?
Because 1 kilometer is exactly 1,000 meters and 1 hour is exactly 3,600 seconds, converting meters per second to kilometers per hour is a direct unit-definition calculation (1,000 m ÷ 3,600 s inverted gives the 3.6 factor), not an empirical or rounded approximation.
Is a nautical mile the same as a regular mile?
No. A nautical mile is exactly 1,852 meters, fixed by international agreement in 1929, while a statute (land) mile is exactly 1,609.344 meters. A nautical mile is roughly 15% longer, which is why knots and mph are different speeds for the same numeric value.
How fast is 100 km/h in mph and m/s?
100 km/h converts to approximately 62.14 mph (dividing by 1.609344) and exactly 27.78 m/s (dividing by 3.6). This is a common reference speed since many countries set highway limits in this range.
References
- National Institute of Standards and Technology (NIST). Special Publication 811: Guide for the Use of the International System of Units (SI), 2008 Edition.
- International Hydrographic Organization. Definition of the international nautical mile (1,852 m), adopted at the Extraordinary International Hydrographic Conference, Monaco, 1929.
- Astin AV, Karo HA. Refinement of Values for the Yard and the Pound. National Bureau of Standards, 1959 (defines the statute mile used for mph).
- International Bureau of Weights and Measures (BIPM). The International System of Units (SI Brochure), 9th edition, 2019 — coherent derived unit m/s.