Speed Converter

Convert between km/h, mph, m/s, knots, Mach, and the speed of light.

62.13711922

Miles/hour (mph)

100 kmh = 62.13711922 mph

100 kmh in all units

Metres/second (m/s)27.77777778
Miles/hour (mph)62.13711922
Knot (kn)53.99572699
Feet/second (ft/s)91.13444153
Mach (at sea level)0.08162972105
Speed of light (c)9.265669311e-8

About Speed Converter

Convert between kilometres per hour, miles per hour, metres per second, knots, Mach, and the speed of light. Select a unit, type a value, and all others update simultaneously. Used by drivers, pilots, physicists, and engineers across different measurement systems.

Speed unit reference

  • km/h — kilometres per hour. Used for road speed limits and weather wind speeds in most countries.
  • mph — miles per hour. The road speed standard in the US, UK, and a few other countries.
  • m/s — metres per second. The SI unit for speed; used in science and engineering calculations.
  • Knots (kn) — nautical miles per hour. The standard speed unit in aviation and maritime navigation worldwide. 1 knot = 1.852 km/h exactly.
  • Mach — ratio to the speed of sound. Mach 1 ≈ 340.29 m/s (1,225 km/h) at sea level and 15°C. Used for aircraft and ballistic speeds. The value varies with altitude and air temperature.
  • Speed of light (c) — approximately 299,792,458 m/s in a vacuum. Used in astrophysics and relativity calculations.

About the Speed Converter

A speed converter translates between common speed units: kilometres per hour (km/h), miles per hour (mph), metres per second (m/s), feet per second (ft/s), and knots. It also includes scientific units like Mach (multiple of the local speed of sound) and the speed of light for context. Speed conversion is a daily need for anyone reading specifications, weather data, or travel information across regions.

This converter shows every unit simultaneously and edits bidirectionally — change any value and the rest update.

Common conversions and where they come up

km/h to mph: most car speedometers show both. Vehicle specifications, racing data, and traffic reports may use either depending on the country. m/s to km/h: physics problems are usually stated in m/s; everyday speeds in km/h. Multiply m/s by 3.6 to get km/h. Knots (nautical miles per hour) are the standard in aviation and marine contexts; 1 knot ≈ 1.852 km/h.

Mach and the speed of sound

Mach number is the ratio of speed to the local speed of sound, which varies with air temperature and density. Mach 1 at sea level in standard atmosphere is about 343 m/s (1,235 km/h); at high altitude it is slower. The converter uses the sea-level standard for the conversion. Real-world supersonic flight calculations require atmospheric data.

How to use the Speed Converter

  1. Enter a speed in any unit

    Every other unit recomputes instantly.

  2. Compare across systems

    Useful when reading a spec in mph and your familiar unit is km/h, or vice versa.

Worked examples

Example 1

Input: 100 km/h

Result: 62.14 mph · 27.78 m/s · 53.99 knots

A typical highway speed.

Example 2

Input: Mach 1

Result: 1,234.8 km/h · 767.3 mph

Speed of sound at sea level, standard atmosphere.

Real-world use cases

  • Reading car or motorcycle specifications across markets.
  • Comparing wind speed reports across weather services.
  • Working out flight or sailing speeds where knots are standard.
  • Solving physics problems that switch units mid-question.

Tips & common mistakes

  • Rough conversion: km/h × 0.62 ≈ mph. mph × 1.6 ≈ km/h.
  • m/s to km/h: multiply by 3.6 — useful for converting physics-class results to everyday units.
  • Knots are not just for boats — aviation uses them for airspeed because nautical miles map naturally to navigation.

Frequently asked questions

Why is Mach not a fixed multiple of km/h?

Because the speed of sound depends on the medium's temperature and density. At 11 km altitude the speed of sound is about 295 m/s; at sea level it is 343 m/s.

What is the speed of light in km/h?

About 1.08 × 10⁹ km/h — a billion kilometres per hour. Included in the converter for scale rather than practical use.

Why is the knot used in aviation?

Historical and practical reasons: one minute of arc of latitude is one nautical mile, so knots map cleanly to navigation calculations.

Related tools

→ Length Converter→ Temperature Converter→ Date Difference

Last updated: June 2026 · All processing happens locally in your browser.