The Formula
km = miles × 1.609344
Exactly — the international mile is defined as 1,609.344 meters. The example above: 10 miles is 16.09 km.
The Mental Shortcut
Multiply by 1.6, or equivalently add 60%: 50 mi → 80 km (exact: 80.5). The Fibonacci sequence works in this direction too: 5 mi ≈ 8 km, 13 mi ≈ 21 km, 34 mi ≈ 55 km — consecutive Fibonacci numbers approximate the ratio because the golden ratio nearly equals 1.609.
Where This Conversion Shows Up
US road trips: a “300-mile drive” is 483 km; the 65 mph speed limit is 105 km/h, and 80 mph on Texas highways is 129 km/h. Running: American race distances — the mile itself (1.61 km), the 10-miler (16.1 km) — and the marathon’s 26.2 miles converting back to 42.2 km. Aviation and weather: US visibility and storm distances arrive in miles; multiply by 1.6 to reason in km.
Frequently Asked Questions
How many km is 1 mile exactly?
1.609344 km — exact by definition since the 1959 international agreement (the mile is 5,280 feet of exactly 0.3048 m each).
What is 26.2 miles in km?
42.16 km — the marathon. The official distance is defined the other way around: 42.195 km, standardized from the 1908 London Olympics course.
How do I convert mph to km/h?
Same factor: mph × 1.609 = km/h. So 30 mph (US city) is 48 km/h, 55 mph is 88.5 km/h, and 70 mph (UK motorway) is 113 km/h.
How long does a 100-mile drive take?
100 mi = 161 km — about 1 h 30 min at highway speeds. For distance-only math this converter is exact; travel time, of course, depends on the road.