MPH to KPH Converter

How to convert miles per hour to kilometers per hour

Converting miles per hour to kilometers per hour is a single multiplication. The formula is mph × 1.60934 = km/h, which means one mile per hour equals 1.60934 km/h. Going the other way, one kilometer per hour equals 0.621373 mph.

The calculator above applies this automatically as you type, but it is worth knowing the arithmetic if you need to sanity-check a figure or work one out without a device to hand.

Worked examples

7 mph to km/h: multiply 7 by 1.60934, which gives 11.26538 km/h.

45 mph to km/h: multiply 45 by 1.60934, which gives 72.4203 km/h.

250 mph to km/h: multiply 250 by 1.60934, which gives 402.335 km/h.

MPH to KPH conversion table

The values below are calculated with the same function as the converter above, so they agree to the digit. Use it as a quick reference when you need a rough figure without typing anything.

What is a mile per hour?

Miles per hour expresses speed as the number of miles covered in one hour. Because a mile is exactly 1.609344 kilometers, the conversion to km/h is exact rather than approximate.

Where the mile per hour came from

The unit came into everyday use with the railways and then the motor car, as both needed a way to post and enforce speed limits. It followed the mile into whichever countries already measured road distance in miles.

Where miles per hour are used today

Speed limits and speedometers use mph in the United States and the United Kingdom. Wind speeds in American forecasts are usually mph, while aviation and shipping use knots instead.

• Residential streets are often 25 to 30 mph
• US highways are typically 65 to 75 mph
• A fast marathon runner averages about 13 mph

What is a kilometer per hour?

Kilometers per hour expresses speed as the number of kilometers covered in one hour. To convert to meters per second, the SI unit of speed, divide by 3.6.

Where the kilometer per hour came from

It spread alongside the kilometer as European countries metricated their road networks through the 19th and 20th centuries. The abbreviation kph is common in English but km/h is the standard form.

Where kilometers per hour are used today

Almost every country posts speed limits in km/h. It is also the standard for weather wind speeds, rail speeds, and vehicle specifications outside the US and UK.

• Urban limits are commonly 50 km/h
• Motorway limits are often 100 to 130 km/h
• A cyclist cruises at about 20 km/h

When you actually need this conversion

miles per hour belong to the imperial / us customary system and kilometers per hour to the metric (si) system, so this conversion turns up whenever information crosses between countries that measure differently.

Accuracy, precision, and rounding

The factor used here (mph × 1.60934 = km/h) is the standard accepted value. The results above are shown to about eight significant figures, which is more precision than almost any practical use requires.

The sensible rule is to round the answer to roughly the same precision as the number you started with. If you measured to the nearest mile per hour, an answer carrying six decimal places is not more accurate, it just looks more accurate. For most everyday purposes one or two decimal places is plenty.

Common mistakes to avoid

Converting in the wrong direction

Multiplying when you should divide is by far the most common error, and it is easy to miss because the result is still a number in a believable range. A quick check: since one mile per hour is 1.60934 km/h, a mile per hour value should get larger when converted.

Using a rounded factor for a long calculation

Rounding the conversion factor before multiplying, then repeating that across many values, compounds the error. Convert with the full factor and round only the final answer.

Converting miles per hour to kilometers per hour in a spreadsheet or in code

A one-off answer is what the calculator above is for. When you have a whole column of figures, or you are writing something that has to do the conversion repeatedly, it is worth putting the formula in the tool you are already working in.

Excel and Google Sheets

With your mile per hour value in cell A1, put this in B1 and fill it down the column:

=A1 * 1.60934

Excel also ships a built-in CONVERT function that handles many unit pairs directly, but it does not cover every unit and its unit codes are easy to mistype. An explicit formula like the one above is harder to get wrong and shows its working.

Python

def mph_to_kmh(value):
    return value * 1.60934

print(mph_to_kmh(10))

JavaScript

const mphToKmh = (value) => value * 1.60934;

console.log(mphToKmh(10));

Store the factor as a named constant rather than typing 1.60934 at each call site. When a figure appears in three places it will eventually be updated in two of them.

The two measurement systems behind this conversion

This conversion sits on the fault line between the two measurement systems still in everyday use. The metric system was designed in one go in the 1790s as a coherent decimal scheme, where every unit relates to the next by a power of ten. The imperial and US customary systems grew instead by accretion over centuries, which is why their relationships are numbers like 12, 16, 5,280, and 43,560 rather than round ones.

Only three countries have not formally adopted the metric system: the United States, Liberia, and Myanmar. In practice the picture is messier than that, since the US uses metric units throughout science, medicine, and the military, while metric countries still buy screens and tires by the inch. That overlap is exactly why conversions like this one stay necessary.

More questions about miles per hour and kilometers per hour

Is the conversion exact or approximate?

The underlying definition is exact, and the factor shown here (1.60934) is that definition expressed to the precision this page displays. For any everyday purpose the result is exact; only at very high precision would you need more digits of the factor.

Why does the answer have so many decimal places?

The converter shows a high-precision result so that it is never the limiting factor in your calculation. It is up to you to round to something sensible. A measurement taken with a tape measure does not become more accurate because the conversion carried six decimals.

Can I convert in the opposite direction on this page?

Yes. The swap button in the calculator reverses the conversion and carries the current result across as the new input, so you do not have to navigate anywhere or retype anything. The second table above also lists the reverse conversion directly.

Does anything get sent to a server?

No. The arithmetic runs in your browser with a few lines of JavaScript. Nothing you type is uploaded, logged, or stored, which also means the converter keeps working if your connection drops after the page has loaded.

Which figure should I use on an official form?

Use whatever precision the form asks for, and if it does not say, match the precision of the original measurement. For height, weight, and similar personal details, one decimal place is almost always sufficient and often more than is wanted.

Related speed conversions

If you need to go the other way as a starting point rather than as a swap, the KPH to MPH converter is the mirror of this page: same factor, same tables, opposite direction. It is the more natural place to start when most of your figures are already in kilometers per hour.

This is a small category, so the list below reaches into the other measurement families as well:

• CM to Inches - Convert centimeters to inches instantly. Enter any value and get the exact result in decimal inches.
• KG to LBS - Convert kilograms to pounds instantly. Perfect for fitness, cooking, and shipping calculations.
• Celsius to Fahrenheit - Convert Celsius to Fahrenheit instantly. Essential for weather, cooking, and science.
• Liters to Gallons - Convert liters to US gallons quickly. Great for fuel economy, cooking, and tank sizes.
• Acres to Square Feet - Convert acres to square feet instantly. Ideal for real estate, land surveying, and property measurements.
• Radians to Degrees - Convert radians to degrees instantly. Essential for mathematics, physics, and engineering.

For anything not listed here, the full converter directory covers over a hundred pairs across length, weight, temperature, volume, area, speed, pressure, energy, and more.

Quick reference

Why Use Our MPH to KPH Converter?

Frequently Asked Questions