Convert between mph, km/h, m/s, knots, Mach and speed of light. Includes fun speed comparisons.
What Is Speed Converter?
A speed converter translates between different velocity units used in everyday life, science, aviation and nautical navigation. The most common conversions are between miles per hour (mph) and kilometres per hour (km/h), but specialised fields use knots (nautical miles per hour), Mach numbers (multiples of the speed of sound), metres per second (m/s) and feet per second.
Different countries and contexts use different speed units. The UK uses mph for road speeds but km/h for athletics. Aviation worldwide uses knots. Physics uses metres per second. Understanding the relationships between these units prevents confusion when travelling internationally, reading scientific literature or following aviation communications.
How to Use This Tool
Enter the speed value you want to convert.
Select the source unit (mph, km/h, m/s, knots, etc.).
Select the target unit.
View the converted result instantly.
See fun speed comparisons to put the number in context.
Tips & Best Practices
A useful approximation: 1 mile ≈ 1.6 km, so multiply mph by 1.6 to estimate km/h.
Mach 1 (the speed of sound) varies with temperature — it is approximately 343 m/s (767 mph) at sea level at 20°C.
Knots are used in aviation and maritime navigation because one knot equals one nautical mile per hour, which relates directly to latitude.
When converting, be precise about whether the wind speed is in knots, mph or km/h — weather services vary by country.
Common Use Cases
Converting between mph and km/h when driving or travelling in different countries.
Translating wind speeds between weather services that use different units.
Converting athletic race speeds between km/h and minutes per mile.
Understanding aviation speeds given in knots or Mach numbers.
Frequently Asked Questions
What units are supported?
Metres per second, km/h, mph, knots, feet per second, Mach and speed of light (Premium).