42 km to miles — 26.10 miles
42 km are exactly 26.10 miles. Multiply by 0.621371 to convert any value from km to miles.
Km to miles
LiveThe formula
Take the number of km and multiply it by 0.621371: 42 × 0.621371 = 26.10 miles. The factor comes from the international definition of the units, so the result is exact rather than an estimate — only the displayed value is rounded.
| Result | 26.10 miles |
|---|
Where this measurement turns up
- Marathon distance
- cycling stages
- day hikes
Worth knowing
A kilometre is 0.621371 miles, which is where the runner's rule of thumb comes from: a 5 km race is a little over three miles, and a marathon's 42.195 km works out at 26.219 miles.
The mistake to avoid
Multiplying by 0.6 instead of 0.621371 understates the mile figure by about three per cent. On a marathon's 42.195 km that turns 26.22 miles into roughly 25.3 miles — visibly wrong to anyone who knows the race distance.
Questions people ask
42 km are exactly 26.10 miles. The calculation is 42 × 0.621371.
Multiply the value in km by 0.621371. To go the other way, divide the miles figure by the same number.
The conversion factor is defined by international standard, so the underlying result is exact. We round the display to a sensible number of decimal places, which is why you may see a slightly shorter figure than a calculator gives.
For a rough estimate, multiply by 0.6 — close enough for everyday use. For anything that needs to be right, such as a form, a cut list or a shipping label, multiply by exactly 0.621371 instead, since the shortcut drifts further from the true value as the number grows.
Need the reasoning, not just the number?
Our guides explain how each measurement is defined, where it is used and which mistakes cost people money.