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Speed Converter

How do I convert speed units?

How it is calculated

Enter a number and choose the unit it is in: km/h, mph, m/s, knots or ft/s. The engine first converts it to metres per second using these factors: km/h ÷ 3.6, mph × 0.44704, knots × 0.514444, ft/s × 0.3048. It then converts from m/s to all five units, so you see every result at once, each with two decimals.

If the unit were not one of those five, the tool falls back to km/h instead of showing an error, so check the selector. Negative values are not blocked and are converted with the same factors. Because the knot factor is rounded to six digits, results in knots are approximate beyond the second decimal.

Worked example

Convert 60 mph. In metres per second: 60 × 0.44704 = 26.82 m/s. Multiplying the unrounded value (26.8224) by 3.6 gives km/h: 96.56 km/h. The same m/s value gives 26.82 ÷ 0.514444 = 52.14 kn and 26.82 ÷ 0.3048 = 88.00 ft/s. The mph figure itself stays at 60.00 mph, which is why 60 mph is a handy rule of thumb: exactly 88 feet per second.

Try this example →

Common mistakes

  • Leaving the unit selector on km/h while typing a value in mph. The numbers look plausible but are off by more than a third.
  • Confusing knots with mph. One knot is about 1.15 mph, and it is a nautical mile per hour, not a land mile.
  • Mixing up m/s and km/h: 10 m/s is 36 km/h, not 10 km/h.
  • Assuming a speed limit sign in another country uses your unit. Check whether it is km/h or mph before converting.
  • Rounding in the middle of a chain of conversions; convert once from the original value instead.

About this calculator

This tool converts a speed value between the five units people actually encounter day to day: kilometers per hour (used on most road signs and car speedometers outside the US), miles per hour (US and UK road speeds), meters per second (the SI unit used in physics and engineering), knots (nautical and aviation speed), and feet per second (some US engineering contexts).

It is used by travelers renting a car abroad and needing to read unfamiliar speed limits, students and engineers converting between metric and imperial in physics problems, and pilots or sailors working with knots alongside ground-based units.

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Comments (1)

  • Editorial team

    All five units are computed through metres per second and rounded to two decimals, so a round trip can drift by a hundredth: 100 mph is 160.93 km/h, and typing 160.93 km/h back in returns 100.00 mph but moves ft/s from 146.67 to 146.66. Keep the original value when you chain conversions. One knot shows as 1.85 km/h. Which unit pairs do you convert most?

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