Why the factor is 2.58998811
A square mile is the area of a square with side 1 statute mile. Since 1 mile = 1.609344 kilometers, then:
1 mi² = (1.609344 km)² = 1.609344 × 1.609344 km² = 2.589988110336 km²
Most websites round this to 2.59 km², which is okay for everyday use. This tool keeps the exact figure but displays reasonable decimals.
Formulas
km² = mi² × 2.58998811
mi² = km² ÷ 2.58998811
FAQ
1. Is this the same as square nautical miles?
No. Nautical miles and statute miles are different. This page uses the US/UK statute mile (1,609.344 m).
2. Can I use this for GIS / mapping?
Yes. Many datasets in the US use mi², while international/UN datasets use km². Use this to switch between them.
3. What precision should I report?
For large regions, 2 decimals in km² is often enough. For engineering / cadastral work, retain at least 4 decimals.