Kilometres to miles (km to mi)

The formula

mi = km × 0.6213711922

Where the factor comes from — each unit by its definition, then its size in SI:

• 1 km = 1000 × m = 1,000 m
• 1 mi = 1760 × yd = 1,609.344 m

Dividing the two SI sizes gives the factor: 0.621371192237 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 1.609344.

Every formula on this site takes lengths in metres. Heights, distances and stopping distances quoted in feet, inches or miles have to be converted first — getting it wrong by a factor of 3.28 is the most common unit slip in homework.

Worked examples

• A sprint track straight (100 m): 0.1 km = 0.0621371 mi — 0.1 × 0.6213711922 = 0.0621371
• A marathon: 42.195 km = 26.2188 mi — 42.195 × 0.6213711922 = 26.2188
• A tall doorway (6 ft): 0.0018288 km = 0.00113636 mi — 0.0018288 × 0.6213711922 = 0.00113636
• A school ruler (30 cm): 0.0003 km = 0.000186411 mi — 0.0003 × 0.6213711922 = 0.000186411

Frequently asked questions