Square Miles to Square Kilometers
An instant square miles-to-square kilometers converter, with the formula and a reference table below.
| Square Miles | Square Kilometers |
|---|---|
| 1 mi² | 2.589988 km² |
| 2 mi² | 5.179976 km² |
| 3 mi² | 7.769964 km² |
| 5 mi² | 12.949941 km² |
| 10 mi² | 25.899881 km² |
| 25 mi² | 64.749703 km² |
| 50 mi² | 129.499406 km² |
| 100 mi² | 258.998811 km² |
How to use
- Enter a value in the Square Miles field.
- The Square Kilometers figure appears immediately — no button to press.
- Typing in the Square Kilometers field converts back to Square Miles the same way.
- Use the reference table for the values that come up most often.
Square Miles to Square Kilometers formula
Converting square miles to square kilometers is a single multiplication by 2.58998811.
km² = mi² × 2.58998811
Why this factor: the square mile and the square kilometer are both defined against the square meter, so dividing one definition by the other gives 2.58998811 directly. Both definitions are set out in full below.
To go the other way, divide by 2.58998811 — or use the Square Kilometers to Square Miles converter, which is the same calculation reversed.
Worked example
Given 50 mi², multiplying by 2.58998811 yields 129.499406 km².
50 mi² × 2.58998811 = 129.499406 km²
The converter above does this for any value you type, in either direction.
What is a square mile?
A square mile is the area of a one-mile square, used for large land areas in the US and UK.
Definition: Exactly 2,589,988.110336 square meters, and exactly 640 acres.
Where it is used: County, state and metropolitan areas, and population density in the US.
What is a square kilometer?
A square kilometer is the area of a one-kilometer square — one million square meters.
Definition: Exactly 1×10⁶ square meters. Note it is the kilometer that is squared, not the prefix applied to a square meter.
Where it is used: City, national park and country areas, population density, and land cover statistics.
Square Miles vs Square Kilometers
The square mile is an imperial unit while the square kilometer is a metric unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many square kilometers are in a square mile?
One square mile equals 2.58998811 square kilometers.
What is the formula to convert square miles to square kilometers?
Multiply the number of square miles by 2.58998811. To reverse it, divide by 2.58998811 instead.
How do I convert square kilometers back to square miles?
Divide by 2.58998811, which is the same as multiplying by 0.386102159.
How many square kilometers are in 10 square miles?
10 mi² works out to 25.899881 km².
How is the square mile defined?
Exactly 2,589,988.110336 square meters, and exactly 640 acres.