KM to Miles Converter

How to convert kilometers to miles

Converting kilometers to miles is a single multiplication. The formula is km × 0.621371 = miles, which means one kilometer equals 0.621371 mi. Going the other way, one mile equals 1.6093445 km.

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 km to mi: multiply 7 by 0.621371, which gives 4.349597 mi.

45 km to mi: multiply 45 by 0.621371, which gives 27.961695 mi.

250 km to mi: multiply 250 by 0.621371, which gives 155.34275 mi.

KM to Miles 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 kilometer?

A kilometer is one thousand meters. It is the standard metric unit for distances too long to state comfortably in meters.

Where the kilometer came from

The kilometer followed directly from the metric system's decimal prefixes; kilo- comes from the Greek khilioi, a thousand. It spread through 19th-century Europe as countries adopted the metric system for trade and cartography.

Where kilometers are used today

Road distances, speed limits, running events, and map scales use kilometers in nearly every country except the United States, the United Kingdom (which still posts road signs in miles), and a small number of others. A 5K and a 10K are races of 5 and 10 kilometers.

• A brisk walk covers about 5 km in an hour
• A standard marathon is 42.195 km
• Central Park is about 4 km long

What is a mile?

A mile is 5,280 feet, or 1,760 yards, or exactly 1.609344 kilometers. The odd-looking 5,280 is a historical accident rather than a designed relationship.

Where the mile came from

The mile comes from the Roman mille passus, a thousand paces, which was about 5,000 Roman feet. England later redefined it to 5,280 feet so that it would contain a whole number of furlongs (eight), the furlong being the unit that actually mattered for ploughing and land measurement.

Where miles are used today

Miles are the road-distance unit of the United States and the United Kingdom, along with a handful of other countries. Nautical miles, a different unit of 1,852 meters, are used in shipping and aviation.

• A mile is roughly a 15 to 20 minute walk
• Four laps of a standard track is just under a mile
• A marathon is 26.2 miles

When you actually need this conversion

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

Accuracy, precision, and rounding

The factor used here (km × 0.621371 = miles) is derived from an internationally agreed exact definition, so the conversion itself is not an approximation. 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 kilometer, 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 kilometer is 0.621371 mi, a kilometer value should get smaller 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 kilometers to miles 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 kilometer value in cell A1, put this in B1 and fill it down the column:

=A1 * 0.621371

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 km_to_mi(value):
    return value * 0.621371

print(km_to_mi(10))

JavaScript

const kmToMi = (value) => value * 0.621371;

console.log(kmToMi(10));

Store the factor as a named constant rather than typing 0.621371 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 kilometers and miles

Is the conversion exact or approximate?

The underlying definition is exact, and the factor shown here (0.621371) 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 length conversions

If you need to go the other way as a starting point rather than as a swap, the Miles to KM 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 miles.

Length conversions rarely arrive alone. A set of dimensions usually mixes scales, so these cover the neighbouring pairs you are likely to need in the same sitting:

• CM to Inches - Convert centimeters to inches instantly. Enter any value and get the exact result in decimal inches.
• MM to Inches - Convert millimeters to inches quickly and accurately. Ideal for engineering, woodworking, and crafts.
• Meters to Feet - Convert meters to feet instantly. Useful for height, room dimensions, and construction measurements.
• CM to Feet - Convert centimeters to feet in one click. Perfect for converting height measurements.
• Inches to Feet - Convert inches to feet quickly. Useful for construction, interior design, and measurements.
• Meters to Yards - Convert meters to yards instantly. Commonly used in sports fields, fabric, and landscaping.

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 KM to Miles Converter?

Frequently Asked Questions