VaneKnots, mph, km/h and m/s: Speed Units Explained
Type a speed in any box and the others follow. Below: where each unit comes from, the exact conversion factors and a table of common speeds.
Updated 1 October 2026
The exact definitions
- Kilometre per hour (km/h): 1,000 metres per hour.
- Mile per hour (mph): one international mile, exactly 1,609.344 metres, per hour. So 1 mph = 1.609344 km/h exactly.
- Knot (kn): one international nautical mile, exactly 1,852 metres, per hour. So 1 knot = 1.852 km/h exactly, or about 1.151 mph.
- Metre per second (m/s): the SI unit. 1 m/s = 3.6 km/h exactly. Phones and GPS receivers report speed in m/s internally, and apps convert it for display.
Quick conversions
| From | Multiply by | To |
|---|---|---|
| km/h | 0.621371 | mph |
| mph | 1.609344 | km/h |
| knots | 1.150779 | mph |
| mph | 0.868976 | knots |
| knots | 1.852 | km/h |
| km/h | 0.539957 | knots |
| m/s | 3.6 | km/h |
| m/s | 2.236936 | mph |
Common speeds
| km/h | mph | knots | m/s |
|---|---|---|---|
| 5 | 3.1 | 2.7 | 1.4 |
| 20 | 12.4 | 10.8 | 5.6 |
| 30 | 18.6 | 16.2 | 8.3 |
| 50 | 31.1 | 27.0 | 13.9 |
| 80 | 49.7 | 43.2 | 22.2 |
| 100 | 62.1 | 54.0 | 27.8 |
| 120 | 74.6 | 64.8 | 33.3 |
| 130 | 80.8 | 70.2 | 36.1 |
| 900 | 559.2 | 486.0 | 250.0 |
Why boats and planes use knots
A nautical mile was originally one minute of arc of latitude along a meridian, so distances on a chart could be read straight off the latitude scale at its side: 60 nautical miles to a degree. The modern nautical mile is fixed at exactly 1,852 metres, close to that average. Because charts, coordinates and distances all line up this way, shipping and aviation kept the knot, and air traffic control, aircraft instruments and marine forecasts still use it worldwide.
That is also why speed over the ground on a boat or in a plane cabin is easiest to compare in knots: the pilot's and the forecast's figures are in knots too. Our online speedometer and the Vane app both switch between km/h, mph and knots.
Sources
- NIST, Guide to the SI, Appendix B: conversion factors (mile = 1,609.344 m; nautical mile = 1,852 m).
- BIPM, The International System of Units (SI Brochure), table of non-SI units including the nautical mile and knot.