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Speed Converter

Convert between km/h, mph, m/s, knots, and feet per second.

About the Speed Converter

The Speed Converter turns a speed written in one unit into the same speed written in another — kilometres per hour to miles per hour, meters per second to knots, feet per second to kilometers per hour, and more. Type a number, pick the two units, and the answer updates as you type. Nothing is sent to a server, so it works offline once the page has loaded.

How to convert km/h to mph

The two units are tied together by an exact definition: one mile is exactly 1.609344 kilometres. This means 1 km/h equals 0.621371 mph.

\\begin{aligned} \\text{mph} &= \\text{km/h} \\times 0.621371 \\\\ \\text{km/h} &= \\text{mph} \\times 1.609344 \\end{aligned}

Worked example. A car travelling at 100 km/h covers 100 × 0.621371 = 62.14 mph. Going the other way, 60 mph is 60 × 1.609344 = 96.56 km/h.

Speed conversion table (km/h to mph)

| km/h | mph | |------|-----| | 10 | 6.21 | | 20 | 12.43 | | 30 | 18.64 | | 50 | 31.07 | | 60 | 37.28 | | 80 | 49.71 | | 100 | 62.14 | | 120 | 74.56 | | 200 | 124.27 |

Other common speed conversions

  • 1 knot = 1.852 km/h exactly, the definition of a nautical mile.
  • 1 ft/s = 0.3048 m/s exactly, because 1 foot = 0.3048 metres.
  • 1 mph = 1.466667 ft/s, used in automotive engineering.

Real-world speed references

| Speed | Unit | Description | |-------|------|-------------| | 5 | km/h | Average walking pace | | 10 | km/h | Easy jog | | 20 | km/h | Cycling on a road | | 30 | km/h | City speed limit (many countries) | | 50 | km/h | Rural road speed limit | | 80 | km/h | Highway speed in many countries | | 100 | km/h | Highway speed in many countries | | 120 | km/h | High-speed highway limit | | 340 | m/s | Speed of sound at sea level | | 1235 | km/h | Speed of sound (Mach 1) | | 299792458 | m/s | Speed of light in vacuum |

Where each unit is used

  • km/h: The standard unit for road speeds worldwide, except in the United States, the United Kingdom, and a few other countries that use mph.
  • mph: Used on road signs and in vehicle speedometers in the United States, the United Kingdom, and some former British colonies.
  • m/s: The SI base unit for speed, commonly used in physics, engineering, and scientific contexts.
  • knots (kn): Used in aviation, maritime navigation, and meteorology. One knot equals one nautical mile per hour.
  • ft/s: Used in some US engineering disciplines and in aviation for vertical speed (feet per minute is more common).

Frequently asked questions

How do I convert 100 km/h to mph?

Multiply by 0.621371: 100 × 0.621371 = 62.14 mph.

How do I convert mph to km/h?

Multiply by 1.609344: 60 mph × 1.609344 = 96.56 km/h.

What is the speed of sound in km/h?

At sea level and 20°C, the speed of sound is approximately 343 m/s, which equals 1235 km/h.

Why do boats use knots?

Historically, sailors measured speed by throwing a log overboard and counting how many knots in a rope passed through their hands in a fixed time. One knot equals one nautical mile per hour, and nautical miles are used because they correspond to minutes of latitude, making navigation easier.

How fast is 100 km/h in mph?

100 km/h equals approximately 62.14 mph.

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