- How many kilometers are in a mile?
- Exactly 1.609344 km. That number doesn't come from measuring anything: in 1959 the US, UK, and other Commonwealth countries agreed that a yard is exactly 0.9144 m, and a mile is 1,760 yards, so 1,760 × 0.9144 = 1,609.344 m. Because it's exact, this converter multiplies by the full 1.609344. Using 1.6 instead reads 0.6% short — about 3.7 km over a 400-mile drive.
- How do I convert miles to km in my head?
- Multiply by 1.6: take the miles, add half, then add a tenth. 50 mi → 50 + 25 + 5 = 80 km; the exact answer is 80.47 km. Another shortcut uses the Fibonacci numbers, which grow by about 1.618 each step: 5 mi ≈ 8 km, 8 mi ≈ 13 km, 13 mi ≈ 21 km, 21 mi ≈ 34 km. From 5 miles up it lands within about 1%; 3 mi ≈ 5 km is the loose one, since 3 mi is really 4.83 km.
- Is a marathon 26.2 miles or 42.195 km?
- 42.195 km is the official distance, set in 1921. In miles that's 26.219 mi, which runners round to 26.2. That rounding is why typing 26.2 here gives 42.16 km, about 30 meters short of the real finish line. The half marathon is 21.0975 km, or 13.109 mi. If you're setting a GPS watch goal, use the kilometer figure; the course is measured in it.
- Is a 5K 3.1 miles?
- Close. A 5K is 3.107 mi, so 3.1 mi is 4.99 km — about 11 meters short. A 10K is 6.214 mi, and 6.2 mi works out to 9.98 km, 22 meters short. On a treadmill set to miles, run to 3.11 for a full 5K and 6.22 for a full 10K.
- Does the same number work for mph to km/h?
- Yes. Speed is distance per hour, and the hour doesn't change, so mph × 1.609344 = km/h. 30 mph is 48.28 km/h, 55 mph is 88.51 km/h, 70 mph is 112.65 km/h. Going the other way is where drivers get caught out: a 100 km/h sign in Canada or Europe is 62.14 mph, not 100. That's why the result card shows the speed line under every conversion.
- What about nautical miles?
- A nautical mile is a different unit: exactly 1.852 km, or 1.151 statute miles. It's used at sea and in aviation because one nautical mile is roughly one minute of latitude, which makes chart navigation easy. Knots are nautical miles per hour. This converter uses statute (land) miles, so don't type nautical miles into it — the answer would come out about 13% low.
- Why do the US and UK still use miles when most of the world uses km?
- Road signs are expensive to replace and drivers are used to them. The UK is officially metric for most things but kept miles and mph on roads; the US never switched road measurement at all. Almost every other country moved to kilometers during the 20th century. So a trip plan from a US map, a UK road sign, or an American running app will hand you miles, and the rest of the world's maps will hand you km.
- Is what I type saved or sent anywhere?
- No. The conversion runs in your browser. Nothing is sent to a server or stored, and closing the tab clears it.
