Free Speed Converter
Convert speed units instantly — km/h, mph, m/s, knots, Mach, ft/s. Type into any field and all others update. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Speed multipliers derive directly from the underlying length and time constants: 1 mph = 1.609344 km/h = 0.44704 m/s (all exact), and 1 knot (one nautical mile per hour) = 1.852 km/h exactly, since the nautical mile itself is fixed at 1,852 meters. Because speed is a ratio of two other units, any rounding in the length or time constant would compound — this converter uses the full-precision base values rather than pre-rounded shortcuts.
Practical Real-World Scenarios
- Aviation and maritime navigation: aircraft and ships report speed in knots, which pilots and sailors then convert to km/h or mph for weather briefings and public communication.
- Automotive: car speedometers in the US show mph while most of the world uses km/h, which matters directly when renting a car abroad or reading imported vehicle specs.
- Sports and athletics: pitch speed in baseball is reported in mph, while soccer and cycling broadcasts internationally use km/h for player and vehicle speeds.
Historical & Technical Background
The knot as a unit of speed dates to 16th-century seafaring, when sailors literally counted knots tied at regular intervals on a rope paid out behind the ship over a fixed time, measured with a sandglass — giving the unit its name. Miles per hour and kilometers per hour are more recent, tied to the standardization of land-based length units and the rise of rail and automobile travel in the 19th and 20th centuries, when speed first became a routinely measured and compared quantity for the general public.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience. Mach is not a fixed unit: this converter uses the speed of sound in dry air at 20 °C, 343 m/s, as a convention.
How This Converter Works
Speed is measured in different units depending on context — km/h and mph for vehicles, m/s for physics, knots for maritime and aviation, and Mach for supersonic speeds. All 6 units update simultaneously.
Common Conversions
| m/s | km/h | mph | Context |
|---|---|---|---|
| 1.4 m/s | 5 km/h | 3.1 mph | Walking speed |
| 4.47 m/s | 16.1 km/h | 10 mph | Cycling speed |
| 27.8 m/s | 100 km/h | 62.1 mph | Highway speed limit (Europe) |
| 44.7 m/s | 160.9 km/h | 100 mph | Fast car on track |
| 343 m/s | 1,235 km/h | 767 mph | Speed of sound (Mach 1, dry air at 20 °C) |