Convert miles per hour to kilometers per hour.

Convert miles per hour (mph) to kilometers per hour (km/h). This is a fixed-ratio conversion — multiply the input by the factor below.

Formula

km/h = mph × 1.60934

Reference values

Things to watch for

• Mph and km/h conversion has no clean ratio; remember 60 mph ≈ 100 km/h works as a rough check.
• Knots (kn) are 1 nautical mile per hour, used in aviation and maritime navigation. 1 kn = 1.852 km/h (exact).
• Mach 1 at sea level standard atmosphere is 343 m/s, but Mach scales with the speed of sound, which varies with altitude and temperature.

What is a mile per hour?

One mile per hour equals exactly 1.609344 km/h or about 0.447 m/s. Vehicle speeds in the US and UK, baseball pitches, and US weather wind speeds.

What is a kilometer per hour?

One kilometer per hour equals exactly 1/3.6 meters per second. Vehicle speeds and speed limits in most countries.

Everyday reference points for mph

It can help to anchor a unit in everyday objects.

• 60 mph — US highway speed.
• 767 mph — speed of sound at sea level.
• 3 mph — a casual walking pace.

How to convert mile per hour to kilometer per hour

To convert a value from mile per hour (mph) to kilometer per hour (km/h), apply the conversion factor shown in the formula above. The calculation is the same whether you do it by hand, in a spreadsheet, or with the live converter on this page.

Steps:

1. Take your input value in mph.
2. Apply the formula km/h = mph × 1.60934.
3. The result is your value in km/h.

For repeated calculations, save the formula in a spreadsheet or use the live converter at the top of this page — it handles the math automatically and displays the result as you type.

Frequently asked questions

How do I convert mph to km/h?

Apply the formula mph → km/h shown above, or just type your value into the converter at the top of this page. The result updates instantly.

Which is bigger, mph or km/h?

This depends on the conversion ratio in the formula. If the factor multiplied by your value gives a larger number, then km/h is the smaller unit (so it takes more of them to express the same quantity). If the result is smaller, then km/h is the larger unit.

When would I use mph versus km/h?

Both units measure speed, so the choice depends on context. Mile per hour is typically used for vehicles, athletic performance, and weather (wind); kilometer per hour similarly. Most professional fields standardize on one or the other based on regional conventions or technical tradition.

How precise is this mph to km/h conversion?

The conversion factor shown is the internationally defined exact value (or the best-published approximation if the relationship is irrational, like degrees-to-radians). The live converter on this page uses double-precision floating-point math, accurate to about 15 significant digits — far beyond any practical engineering need.

Is the conversion ratio exact, or an approximation?

Most unit conversions between SI metric units, and between SI and US customary units, have been formally defined as exact values since the 1959 international yard-pound agreement and subsequent SI redefinitions. Exceptions are unit pairs that involve irrational numbers (radians, e.g.) or empirical conversions (like food calories, which depend on temperature). When in doubt, consult the formula at the top of this page.

Related conversions

See also