What is Precise Miles ↔ Kilometers Converter?
miles to km, road distance This tool runs entirely in your browser. No data is sent to any server, and no signup is needed.
Miles to Kilometers Converter
Miles to kilometers: 1 mile = 1.609344 km exactly. Used in road distance, athletics, vehicle speed.
About this converter
The international mile is exactly 1.609344 kilometres, defined by the 1959 International Yard and Pound Agreement. That makes mile to kilometre conversion exact, not approximate. The metre itself is defined via the speed of light (BIPM 2019 redefinition); the mile inherits its precision from the metre.
How it works
The 1959 International Yard and Pound Agreement fixed:
1 yard = 0.9144 m (exact)
1 mile = 1,760 yards
= 1,760 x 0.9144
= 1,609.344 m
= 1.609344 km (exact, NIST SP 811)
1 km = 1 / 1.609344
= 0.6213711922 miles
To convert: multiply miles by 1.609344 to get kilometres; multiply kilometres by 0.6213711922 to get miles. The reverse factor is irrational; keep enough digits for the precision you need.
Worked example
A US driver crosses into Canada and sees a speed-limit sign reading 100 km/h on the highway. They want to know the equivalent in mph and whether their 65 mph cruise speed is too fast.
- Convert 100 km/h to mph: 100 x 0.6213711922 = 62.137 mph.
- Driver's habitual cruise: 65 mph x 1.609344 = 104.61 km/h.
- Speed margin over the posted limit: 104.61 - 100 = 4.61 km/h ~ 2.86 mph.
- Quick mental check: every 60 mph is about 96.6 km/h, so 65 mph is roughly 105 km/h. Matches.
Reference table
| Miles | Kilometres | Context |
|---|---|---|
| 0.621 | 1 km | 10-minute brisk walk |
| 1 | 1.609 km | Standard US mile |
| 3.107 | 5 km | 5K race / parkrun |
| 6.214 | 10 km | 10K race |
| 13.109 | 21.097 km | Half-marathon |
| 26.219 | 42.195 km | Marathon |
| 62.137 | 100 km | Highway speed limit (km/h to mph) |
| 238,855 | 384,400 | Earth-to-Moon mean distance |
Common pitfalls
- Mile vs nautical mile. 1 statute (land) mile = 1.609344 km. 1 nautical mile = 1.852 km, by international definition, used in maritime and aviation contexts. Confusing them creates a 15 percent error. Aircraft cruise speeds in "knots" are nautical miles per hour.
- US survey mile vs international mile. Until 2023, US federal surveying used a survey mile of 1,609.347218694 m, a 3.2 mm difference per mile. For a 1,000 mile baseline, that's 3.2 m. NIST officially retired the survey mile on 1 Jan 2023; all modern GPS, road, and federal mapping use the international mile.
- mph and km/h flip when speed limits are reported. A "70 limit" in the US means 70 mph (112.65 km/h). A "70 limit" in Germany means 70 km/h (43.5 mph). Confusing the unit at the border creates a 60 percent over/under speed error.
- Marathon math: 26 miles is NOT 26.0 miles. A marathon is 26.219 miles = 26 miles 385 yards, not 26 even. The 0.219 mile = 385 yards comes from the 1908 London Olympics. Saying "I ran 26 miles" undercounts by 385 yards.
- Vehicle fuel economy units. US mpg uses statute miles per US gallon; UK mpg uses statute miles per Imperial gallon (4.546 L vs 3.785 L). UK mpg figures are ~20 percent higher for the same fuel use because the Imperial gallon is bigger. European L/100 km is the inverse of mpg.
Related tools and references
Frequently asked questions
Is 1 mile exactly 1.609344 km?
Yes. The international mile is defined as exactly 1,609.344 metres = 1.609344 km, by the 1959 International Yard and Pound Agreement signed by the US, UK, Canada, Australia, New Zealand, and South Africa. The factor is exact, not an approximation. NIST SP 811 lists the same value.
What is the difference between the international mile and the US survey mile?
The international mile = 1,609.344 m exactly. The US survey mile = 1,609.347218694 m, slightly longer by about 3.2 mm in a mile. The US survey mile was deprecated for federal use on 1 Jan 2023 (NIST), so all modern road, GPS, and athletic distances use the international mile.
How long is a marathon in miles and kilometres?
The official marathon distance, fixed by the IAAF (now World Athletics) in 1921, is 42.195 km, equal to 26.21875 miles, or 26 miles 385 yards. The exact yards-and-feet origin comes from the 1908 London Olympics, when the course was lengthened so the royal box would have a clear finishing view.
Which countries still use miles for road distances?
Only the United States, the United Kingdom, and Liberia post road distances in miles. Myanmar uses both. Every other country posts kilometres. The UK kept miles for road signage when it metricated other measures because changing every distance plate would cost billions of pounds.
Sources
- International Yard and Pound Agreement (1959), definition of 1 yd = 0.9144 m.
- NIST Special Publication 811 (2008) Guide for the Use of the International System of Units, App. B.8.
- NIST Federal Register Notice (2020) retiring the US survey foot / mile, effective 1 Jan 2023.
- World Athletics (formerly IAAF) marathon distance standard, 42.195 km since 1921.