Kilometers and miles — reading road signs across borders
1 mile is 1.609344 km. That single factor governs every speed limit, distance sign and fuel-economy sticker you will ever see on a road.
The mile survived colonial mapping, imperial engineering and the American Interstate system. The kilometre took over almost everywhere else. Cross the wrong border without doing the math and a 60 mph highway cruise turns into a 96 km/h speeding ticket.
The exact factors
1 mi = 1.609344 km (exact) > 1 km = 0.621371 mi > 60 mph ≈ 96.56 km/h; 100 km/h ≈ 62.14 mph
The 5/8 mental trick
5 miles ≈ 8 km — accurate to 0.4%. To convert km to miles, multiply by 5 and divide by 8. To convert miles to km, multiply by 8 and divide by 5. A 200 km sign is 200 × 5/8 = 125 mi (actual: 124.3).
Speedometer tolerances
UN Regulation 39 requires speedometers to never under-read. Most modern cars over-read by 2–5%. A GPS speed of 100 km/h can show 103–105 on the dash. When your speedometer has both scales, the primary one is legally binding — the secondary one is a courtesy.
Worked example — a US visitor in the EU
A US driver used to 65 mph on the highway crosses into France where the limit is 130 km/h. 130 × 5/8 = 81 mph — 16 mph faster than they are used to. Going the other way, a European used to 130 km/h on a US freeway posted at 70 mph is being asked to drop to 113 km/h — a 13% slowdown that feels unnatural.
The five-second recap
Multiply miles by 1.609 for km. Multiply km by 0.621 for miles. Or use 5-for-8. And always trust the primary scale on your speedometer.
Try the converters mentioned in this article
FAQ
How many km in a mile, exactly?+
1.609344 km. This factor is exact by international agreement.
Why is a nautical mile different?+
The nautical mile (1.852 km) is based on one minute of latitude. The statute mile used on roads has no astronomical basis.
Do UK road signs use km or miles?+
Miles. The UK is one of the few countries that officially retains the mile on road signage.
This article was written by The Turbo Unit Converter engineering desk (Transport & navigation) and last reviewed on 2026-06-28 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.