What this calculator does
Change a speed from one unit to another, like miles per hour to kilometers per hour. A speed is a distance divided by a time. So every speed unit is built from a length unit and a time unit. The inch, foot, mile and nautical mile all have exact metric sizes. That makes conversions between miles per hour, kilometers per hour, knots and meters per second exact too.
Enter a speed and choose the two units. The converter shows the result and the working through meters per second. It also shows a table of the same speed in every unit. A Mach figure (a multiple of the speed of sound) is included for reference, clearly marked as an estimate.
Where it's used
Why this math matters outside the classroom:
- Driving abroad. A 50 km/h city speed limit is about 31 mph.
- Speed of sound. Sound in air at room temperature travels about 343 m/s, which is about 1,235 km/h.
- Ferries. A ferry at 18 knots travels about 33.3 km/h.
- Baseball. A 90 mph fastball is moving at 132 ft/s.
- Physics labs. A cart timed at 2.5 m/s is moving at 9 km/h.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the speed. Zero and decimals are allowed, but negative speeds aren't.
- Choose the unit you're converting from and the unit you want.
- Read the converted value, or scan the table for all units at once. The working shows how big each unit is in meters per second.
What the inputs mean
- Speed
- The speed to convert, in the “From” unit.
- From
- The unit your number is in. Mach here means a multiple of the standard speed of sound at sea level.
- To
- The unit you want the answer in.
Formula and method
result = value × (from-unit in m/s) ÷ (to-unit in m/s) 1 km/h = 1,000 m ÷ 3,600 s = 0.27777… m/s 1 mph = 1,609.344 m ÷ 3,600 s = 0.44704 m/s 1 knot = 1,852 m ÷ 3,600 s = 0.51444… m/s 1 ft/s = 0.3048 m/s; Mach 1 ≈ 340.294 m/s (sea-level standard atmosphere)
In the formulas, m is meters, s is seconds and m/s is meters per second. Each unit is stored as its size in meters per second. The converter multiplies by the from-unit's size to get meters per second. Then it divides by the to-unit's size.
Mach works differently. The speed of sound depends on air temperature, so Mach 1 isn't a fixed speed. This tool uses the value for the standard reference atmosphere (the International Standard Atmosphere) at sea level and 15 °C. That's about 340.3 m/s. At cruising altitude the air is colder, and Mach 1 is noticeably slower.
Worked example
Convert a highway speed of 60 mph to kilometers per hour.
- 60 mph × 0.44704 = 26.8224 m/s.
- 26.8224 m/s ÷ (1,000/3,600) = 96.56064 km/h.
Result: 60 mph is 96.56064 km/h, a little under 97 km/h.
Understanding the result
For quick estimates, 1 mph is about 1.6 km/h and 1 knot is about 1.15 mph. And 1 m/s is exactly 3.6 km/h.
Treat Mach figures as a rough guide only. A real Mach number comes from the speed of sound in the air the object is actually moving through.
Assumptions and limitations
- Miles, feet and nautical miles use their international definitions.
- Mach uses the standard sea-level (ISA) speed of sound, 340.294 m/s.
- The Mach value is approximate. It ignores altitude, temperature and humidity.
- It converts how fast only. It doesn't handle direction or negative velocities.
- Pace units, such as minutes per mile, aren't included.
Frequently asked questions
How do I convert km/h to m/s in my head?
Divide by 3.6. One kilometer per hour is 1,000 meters in 3,600 seconds, so 90 km/h is 25 m/s. To go the other way, multiply by 3.6.
What exactly is a knot?
A knot is one nautical mile per hour. A nautical mile is exactly 1,852 meters, so one knot is exactly 1.852 km/h, or about 1.15 mph. It's the standard speed unit at sea and in aviation.
Why is the Mach number marked approximate?
The speed of sound changes with air temperature. Mach 1 is around 761 mph at sea level on a standard 15 °C day. It's closer to 660 mph in the cold air where airliners cruise. One fixed value can only be a reference point.
Is mph the same in the US and the UK?
Yes. Both use the international mile of 1,609.344 meters, so miles per hour mean the same speed in both countries.
Is there a page for a single pair, such as mph to km/h?
Yes. Popular speed pairs have their own pages, each with a table of typical speeds. They cover miles per hour to kilometers per hour, knots to miles per hour, and meters per second to kilometers per hour.
How this calculator is checked
Method: International yard (0.9144 m) and nautical mile (1,852 m) definitions; ISA sea-level speed of sound 340.294 m/s for the approximate Mach entry. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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