KPH to MPH Converter (km/h to mph)

What does this calculator do?

This converter turns kilometres per hour (km/h, also written kph or kmh) into miles per hour (mph), and back. Type a number and the result updates as you type: the converted speed, the same speed in metres per second and — for anything between 3 and 30 km/h — the matching running pace per kilometre and per mile.

Typical uses: reading a speed limit or a car speedometer abroad (120 km/h on a French autoroute, 70 mph on a UK motorway), setting a US treadmill that only shows mph, or comparing a cycling or running speed from a European app with an American one. The three charts under the converter cover road speeds, running speeds with pace, and mph to km/h, so the common values are readable without typing anything.

How does it work?

There is only one fact behind the page: since 1959 the international mile has been defined as exactly 1,609.344 metres. A speed in miles per hour is therefore a speed in kilometres per hour divided by 1.609344, and the reverse is a multiplication. Because both units measure distance per hour, the time part cancels out — no minutes or seconds are involved in the conversion itself.

The page keeps the full-precision value internally and rounds only for display, to two decimals. Metres per second come from km/h ÷ 3.6 (1,000 m in 3,600 s). Running pace is the reciprocal of speed: 3,600 seconds divided by km/h gives seconds per kilometre, the same identity the pace converter uses.

Formula

mph  = km/h ÷ 1.609344   (≈ km/h × 0.621371)
km/h = mph × 1.609344
m/s  = km/h ÷ 3.6
pace (s/km)   = 3600 ÷ km/h
pace (s/mile) = 3600 ÷ mph

0.621371 is 1 ÷ 1.609344 rounded to six decimals — accurate to better than one part in a million, far below what any speedometer can show. For mental arithmetic, “multiply by 5, divide by 8” (× 0.625) is within 0.6%, and “× 0.6” reads about 3.4% low.

Worked example

How to interpret the result

The answer is exact: 100 km/h really is 62.14 mph. The question is usually what you compare it with. Road signs in the US and UK are in mph; almost everywhere else uses km/h, and many car dashboards show both scales. A treadmill set to 6.0 mph is 9.66 km/h, which is a 6:13 /km or 10:00 /mile pace — the running chart lists the usual training range so you can go straight from a belt setting to a pace.

Searches like “km/h to mph/h” or “km/h in miles/h” mean the same thing as kph to mph: mph already contains “per hour”, so there is no extra “/h” to add. Knots are a different unit (nautical miles per hour, 1 knot = 1.852 km/h) and are not what this page converts.

Assumptions and limitations

Assumptions

• Miles are international statute miles of exactly 1.609344 km. The former US survey mile (retired in 2023) differs by about 3 mm per mile — invisible at two decimals.
• The number you type is already in the unit selected next to it.
• Running pace assumes the speed is held constant over the whole kilometre or mile.

Limitations

• Results are rounded to two decimals, so converting a rounded result back can be 0.01 off the starting value.
• The page converts the number you enter; it does not correct speedometer, GPS or treadmill calibration error, which is often a few percent.
• Pace is only shown between 3 and 30 km/h — outside that range it is not a meaningful running figure.
• Knots, metres per minute and feet per second are not offered as inputs; use metres per second (shown in the result) as the bridge.

Methodology and sources

Method type: Exact calculation

A definition, not a model: the converter is exact arithmetic on the international mile (1 mile = 1.609344 km) and 1 km/h = 1/3.6 m/s. The only approximation is rounding the display to two decimals and pace to the second.

• Methodology: Speed and unit conversion
• Methodology: Rounding and displayed precision

Sources: NIST SP 811

Last reviewed: October 9, 2026