Miles to km:
convert road distances, speed limits and odometers

How many kilometres are in a mile?

One mile is exactly 1.609344 kilometres. The figure is defined, so it is as precise as you want to make it.

Road signs in the United States and the United Kingdom show miles, and so do the speedometers on most cars sold there. Visitors who are used to kilometres have to convert every distance and speed they read.

For mental maths, 1.6 is the number to remember. Sixty miles is 96 km by that rule, against the exact 96.56 km, and the shortcut errs by less than 1%.

This guide covers the conversion as a driver or traveller meets it: distances on signs and maps, speed limits, rental-car odometers and service intervals. For race distances and pace, the km to miles article takes the opposite direction.

Miles to km formula and a mental route

1. 1Take the distance in miles.
2. 2Multiply by 1.609344 on a calculator, or by 1.6 in your head.
3. 3If you used 1.6, add about 0.6% for the exact answer.
4. 4Round to the nearest kilometre for travel plans.

• 5 miles = 8.05 km
• 10 miles = 16.09 km
• 20 miles = 32.19 km
• 50 miles = 80.47 km
• 500 miles = 804.67 km

Values you cannot find in a list can be assembled from smaller ones. For 35 miles, add 20 miles (32.19 km), 10 miles (16.09 km) and 5 miles (8.05 km) to get 56.33 km, which matches the exact 35 × 1.609344.

Choose the level of accuracy to suit the job. Use 1.6 while driving, 1.609 for planning a route, and the full 1.609344 when you record a distance.

A fraction also works. Multiply the miles by 8 and divide by 5. For 40 miles, that is 40 × 8 ÷ 5 = 64 km, against 64.37 km exactly.

Worked example: a 250-mile road trip

You are planning a 250-mile drive and the satellite navigation in your rental car shows kilometres. You also want to know how long the trip takes at 65 mph.

Electric cars are sometimes advertised with a range in miles. A car with a 300-mile range can cover 482.8 km, so a 450 km trip is within range on paper, though real range varies with speed and weather.

Signs work the same way. '30 miles to the next town' is 48.3 km, and an exit in half a mile is 0.8 km, or about 805 m. Use the 1.6 shortcut while driving and leave the exact figure for planning.

The journey time does not change with the unit, so it is a good test of your conversion. Divide 402.3 km by 104.6 km/h and you again get 3.85 hours.

Speed limits in mph and km/h

Short distances on UK road signs can be in yards. A yard is 0.9144 m, so 880 yards, which is half a mile, is 804.7 m. A quarter mile is 440 yards, or 402.3 m.

Memorise a few pairs: 30 mph is 48 km/h, 50 mph is 80 km/h, 60 mph is 97 km/h and 70 mph is 113 km/h. They cover most roads you will meet and give you a sense of speed at a glance.

Time is the other number that people want from a speed. A 100 km stretch at 65 mph takes 100 ÷ 104.6 = 0.956 hours, or about 57 minutes.

The last column is only a rough guide to where such numbers appear. Limits vary by country, state and road, so follow the signs rather than this table.

Odometers, service intervals and rentals

A rental car's odometer often reads in miles. A 5,000-mile service interval is 8,046.7 km, and a 120-mile daily limit is 193.1 km.

A tank that lasts 350 miles will last 563.3 km, which helps when a navigation app lists fuel stops in kilometres. If your employer reimburses travel per kilometre, convert the miles on a foreign receipt before you submit the claim.

Rental charges per mile convert in the same way, but by dividing. If a hire company charges 0.30 per mile beyond the allowance, that is 0.30 ÷ 1.609344 = 0.186 per kilometre.

Trail maps in the US use miles as well. A 6.5-mile trail is 10.46 km. Add the legs of a route in miles first: 123 + 87 + 45 miles is 255 miles, or 410.4 km, which is cleaner than converting each leg and adding rounded numbers.

When you buy a used car from abroad, convert the odometer and compare it to a local car: 60,000 miles is 96,560 km.

Fuel economy has a similar trap, because the gallon is a unit that changes with the country. That is covered in the next section.

Nautical miles and miles per gallon

A nautical mile is exactly 1.852 km, which is about 1.15 statute miles. Flights and ships quote speed in knots, which is one nautical mile per hour, so 20 knots is 37.04 km/h.

Fuel economy needs two conversions at once, because the gallon is a unit too. A US gallon is 3.785 L and an imperial gallon is 4.546 L. So 30 mpg is 12.75 km/L on the US gallon, and 10.62 km/L on the imperial one.

Always check which gallon a manual uses before you compare cars.

Mistakes with miles to km

• Dividing by 1.609 instead of multiplying. 100 miles is 160.9 km, not 62.1 km.
• Applying the conversion to the speedometer reading twice. If the display already shows km/h, do not convert again.
• Rounding 1.609 to 1.5. A 100-mile trip would come out at 150 km, which is more than 10 km short.
• Treating mpg as a distance unit. It combines a distance and a volume.
• Converting a price per mile by multiplying. A price per distance goes the other way: divide by 1.609344 to get the price per kilometre.

If you drive in a country that uses miles, change the navigation units to miles as well. Matching units on the screen and on the road signs removes most conversion errors.