Speed Converter

Convert speed between mph, km/h, m/s, knots, and more.

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Convert speed between miles per hour, kilometers per hour, meters per second, feet per second, knots, and Mach instantly.

How It Works

How Speed Converter Works

Every speed unit is first converted to a common base unit — meters per second — using its fixed conversion factor (for example, 1 mph = 0.44704 m/s, 1 knot = 0.514444 m/s). This common intermediate step means any unit can be reliably converted to any other without needing a separate formula for every possible pairing.

Once the value is in meters per second, it's converted to the target unit using that unit's own factor in reverse. Mach is treated as a fixed multiple of the speed of sound at sea level (about 340.29 m/s) for a simple approximate conversion, though the true speed of sound varies with altitude and temperature.

Worked Example

See It In Action

60 mph converts to 96.56 km/h (60 × 1.60934), or equivalently 26.82 m/s and about 52.14 knots.

Real-World Use Cases

Who Uses Speed Converter and Why

Converting a car's posted speedometer reading between mph and km/h when driving in a country that uses the other system.
Working out a wind or flight speed reading given in knots into a more familiar mph or km/h figure.
Converting a lab or physics measurement given in meters per second into a more intuitive everyday unit.
Checking how a speed given in Mach compares roughly to mph or km/h for context.

Common Mistakes

Mistakes to Avoid

Treating a Mach conversion as an exact, aviation-grade figure — this converter uses a standard sea-level approximation for the speed of sound, but the real speed of sound actually shifts with air temperature and altitude, so a precise aviation calculation needs those specifics.
Confusing knots with mph — a knot is one nautical mile per hour, which is a different distance basis than the statute mile mph uses, so the two aren't interchangeable without conversion.
Assuming feet per second and mph are close enough to eyeball — they differ by a factor of roughly 1.47, which is easy to misjudge without actually converting.

Pro Tips

Tips for Best Results

For marine or aviation contexts, knots is the standard unit — converting a knots figure to mph or km/h can make it easier to reason about in everyday terms, but keep the original knots figure for anything navigation-related.
If you need Mach for a real aerospace or engineering calculation rather than a rough comparison, use a value that accounts for the actual altitude and temperature rather than this sea-level approximation.

Troubleshooting

Fixing Common Problems

My Mach conversion doesn't match a figure I've seen elsewhere for the same speed. — The speed of sound depends on air temperature and altitude, so a source using different atmospheric assumptions than this tool's sea-level approximation will show a slightly different Mach value for the same actual speed.

Glossary

Terms Explained

Knot: A unit of speed equal to one nautical mile per hour, standard in marine and aviation navigation rather than everyday road use.

Mach: A ratio of speed to the local speed of sound — Mach 1 equals the speed of sound at the given conditions, which this converter approximates at sea level.

FAQ

Frequently Asked Questions

Is the Mach conversion exact?

It's a fixed approximation based on the speed of sound at sea level and standard temperature. The actual speed of sound decreases at higher altitudes and varies with air temperature, so real Mach speed calculations in aviation account for those factors more precisely.

What is a knot, and where is it used?

A knot is one nautical mile per hour (about 1.15 mph), and is the standard speed unit used in marine navigation and aviation worldwide.

Why convert everything through meters per second first?

Using one common "base" unit means the calculator only needs to know each unit's conversion factor to meters per second, rather than needing a separate formula for every possible pair of units — it's simpler and less error-prone.