Conversion Runs locally Ready to use Built-in examples No tracking

Speed Converter

Convert between km/h, m/s, mph, knots, ft/s and Mach number with exact conversion factors and common reference values.

Road speed is quoted in km/h, in mph in the US and UK, in knots at sea and in the air, in m/s in physics, and in Mach number near the speed of sound — every setting has its habit. This tool converts between km/h, mph, m/s, knots and Mach number; the anchors are 1 m/s = 3.6 km/h exactly, 1 knot = 1.852 km/h and Mach 1 ≈ 1225 km/h at sea level and 15 °C.

Mach number depends on the temperature and altitude of the medium: an airliner cruising at Mach 0.85 has a ground speed of roughly 900 km/h, while Mach 0.85 at sea level is 1041 km/h — this tool converts against sea-level standard conditions and says so. And road speed limits and navigation both use km/h, so do not read an mph figure as km/h; the difference is 60%.

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How to use

  1. Enter the speed and choose its unit.
  2. Read the value in the other units.
  3. Note that Mach is computed for sea-level standard conditions.
  4. Keep mph and km/h distinct — the gap is 60%.

How it works

Speed conversion rules

Core conversion: 1 m/s = 3.6 km/h. For example 100 km/h is about 27.78 m/s; a 120 km/h highway limit is about 33.33 m/s.

Miles per hour

Miles per hour: 1 mph = 1.609 km/h. A US 65 mph highway is about 104.6 km/h.

Converting knots

Knots (kn), for sea and air: 1 knot = 1.852 km/h (one nautical mile per hour). A large airliner cruises around 900 km/h, about 486 knots, roughly Mach 0.78.

Code example

JavaScript km/h as the hub 

const KMH = { kmh: 1, mph: 1.609344, ms: 3.6,
              kn: 1.852, mach: 1225.056 };   // sea-level speed of sound

const convert = (v, from, to) => v * KMH[from] / KMH[to];

convert(120, "kmh", "mph");    // 74.6
convert(0.8, "mach", "kmh");   // 980 (at sea level)

Python The same coefficients in Python 

KMH = {"kmh": 1, "mph": 1.609344, "ms": 3.6, "kn": 1.852}

convert = lambda v, f, t: v * KMH[f] / KMH[t]

convert(27.8, "ms", "kmh")   # 100.08
convert(15, "kn", "kmh")     # 27.78 (a boat's speed)

FAQ

Why does 1 m/s equal 3.6 km/h?

1 hour = 3600 seconds and 1 km = 1000 m, so 1 m/s = 3600 m/h = 3.6 km/h. Remember "meters per second times 3.6" for a quick conversion.

What is a knot?

A knot is 1 nautical mile per hour = 1.852 km/h, historically measured with a knotted line. It's used for ships and aircraft, e.g. an aircraft carrier at 30 knots is about 55.6 km/h.

What is Mach number?

Mach = speed / local speed of sound. At sea level and 15 C the speed of sound is about 340.3 m/s, so Mach 1 is about 1225 km/h. Airliners cruise at about Mach 0.78-0.85.

How do km/h and m/s convert?

1 m/s = 3.6 km/h. Divide km/h by 3.6 for m/s, multiply m/s by 3.6 for km/h. The 3.6 comes from "3600 seconds per hour / 1000 meters." For example a 120 km/h limit is about 33.3 m/s.

What's the difference between "mai," "yard" and km/h?

"Mai" is a transliteration of mile, so 1 mai is about 1.609 km/h; a "yard" is a length unit, 1 yard is about 0.914 m, unrelated to speed. Colloquially in China "driving 80 mai" usually means 80 km/h, which is technically inaccurate and best not mixed.

How do pace and speed convert?

Pace (minutes per kilometer) and speed (km/h) are reciprocal: speed = 60 / pace. For example a 5:30 pace (5.5 min/km) is 60 / 5.5, about 10.9 km/h. Runners use pace; treadmills often show speed.

How do wind-force levels map to m/s?

See the Beaufort scale: level 3 is 3.4-5.4 m/s, level 6 is 10.8-13.8 m/s, level 12 is 32.7 m/s or more. A forecast "gusts to force 8" means instantaneous wind, higher than the average — convert to m/s to compare.