Speed Converter — km/h to mph, Knots & m/s Free
Convert speed units online free — kilometers per hour to miles per hour, knots, meters per second, Mach number and more. Instant conversion, no sign-up required.
Last updated: June 2026
Common speeds
- Brisk walk
- 5 km/h · 3.1 mph
- Car on a highway
- 120 km/h · 75 mph
- Speed of sound
- 343 m/s · 1,235 km/h
About this tool
Convert speed across every common unit
Speed limits, weather reports, sports stats and physics problems all use different units, and switching between them by hand is error-prone. This speed converter shows the most common units together — kilometres per hour, miles per hour, metres per second, feet per second, knots and Mach — and updates them all the moment you type into any one box.
The everyday pairing is km/h and mph, useful when driving across borders or reading car specs from another market; one mile per hour is about 1.609 km/h. Scientists and engineers tend to work in metres per second (multiply by 3.6 to get km/h), pilots and sailors use knots (one nautical mile per hour), and aviation uses the Mach number, the ratio to the local speed of sound.
To give a sense of scale, the tool lists familiar reference speeds — a brisk walk, highway driving and the speed of sound — so any result is easy to picture. The Mach figure uses the standard sea-level speed of sound (about 343 m/s), since the real value varies with air temperature and altitude. Everything is computed locally in your browser, making the converter instant, free and completely private.
How it works
Three quick steps — no account, nothing uploaded to a server.
Type a speed
Enter a value in any unit — km/h, mph, m/s and more.
See every unit
All the other units convert at the same instant.
Compare the scale
Use the common-speed references to picture the result.
FAQ
Frequently asked questions
How do I convert km/h to mph?
Multiply kilometres per hour by about 0.6214 to get miles per hour (since one mile is 1.609344 km). For example, 100 km/h is roughly 62.1 mph. Type into the km/h box and the mph box updates instantly.
How fast is the speed of sound?
At sea level in dry air around 20 °C, sound travels at about 343 metres per second — roughly 1,235 km/h or 767 mph. That speed is the basis of the Mach number, so Mach 1 is the speed of sound. The converter's Mach unit uses this sea-level value.
What is a knot?
A knot is one nautical mile per hour, equal to exactly 1.852 km/h or about 1.151 mph. It's the standard speed unit in aviation and maritime navigation because it ties directly to latitude and nautical charts.
What does Mach mean?
Mach number is speed expressed as a multiple of the local speed of sound. Mach 1 is the speed of sound, Mach 2 is twice that, and so on. Because the speed of sound changes with air temperature and altitude, this converter uses the standard sea-level value as a reference.
How do I convert m/s to km/h?
Multiply metres per second by 3.6 to get kilometres per hour. So 10 m/s is 36 km/h. Conversely, divide km/h by 3.6 to get m/s. The converter handles both directions automatically — just type in either box.
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