Square KM to Square Miles Converter
Convert square kilometers (km²) to square miles (sq mi) instantly. Type a value — the result updates as you type, and the swap button converts the other way.
Square km to Square Miles formula
sq mi = km² ÷ 2.589988110336
1 square kilometer = 0.3861 square miles · 1 square mile = 2.59 square kilometers
To convert square kilometers to square miles, divide the value by 2.589988110336. For example, 100 km²:
sq mi = 100 ÷ 2.589988110336sq mi = 38.610216
So 100 km² = 38.61 sq mi.
Mental math shortcut
Quick mental estimate: multiply by 0.4. For 100 km² that gives about 40 sq mi — off by 1.39 sq mi (3.6%). Use the exact formula when precision matters.
Square km to Square Miles conversion table
Square Miles back to Square km
The same values converted the other way, rounded for everyday use:
| Square miles | Square kilometers |
|---|---|
| 0.3861 sq mi | 1 km² |
| 3.86 sq mi | 10 km² |
| 19.31 sq mi | 50.01 km² |
| 38.61 sq mi | 100 km² |
| 193.05 sq mi | 500 km² |
| 386.1 sq mi | 999.99 km² |
| 3861.02 sq mi | 10000 km² |
About the units
Square kilometers (km²)
A square kilometer is one million square meters, about 0.386 square miles or 247 acres.
Square miles (sq mi)
A square mile is 640 acres or about 2.59 square kilometers.
Frequently asked questions
How many square miles are in a square kilometer?
One square kilometer equals 0.3861 square miles.
What is 100 Square km in Square Miles?
100 km² = 38.61 sq mi.
How do I convert Square Miles back to Square km?
Multiply the square miles by 2.589988110336.