About the Square Miles to Square Kilometers
This square miles to square kilometers converter turns large land areas between the US customary square mile and the metric square kilometre, and shows the same area in acres, hectares, square metres and square feet. Enter a value in any of the four main units and every equivalent appears at once.
It is useful for comparing the size of cities, counties, national parks, wildfire perimeters, lakes and farms when one source uses square miles and another uses km², for geography homework, and for reading land listings or planning documents from another country.
The calculation uses the international mile of exactly 1,609.344 m, so one square mile is exactly 2.589988110336 km² and exactly 640 acres. The older US survey mile, obsolete since 1 January 2023, is about 0.0004% larger in area — a difference that only matters for legacy land-survey records.
With the default inputs, the converted area is 2.59. Change any value above to recalculate instantly.
How to use the square miles to square kilometers
- 1Enter the area you want to convert.
- 2Choose whether it is in square miles, square kilometres, acres or hectares.
- 3Read the converted area and every other unit.
- 4Use the reference table for quick round-number conversions.
Formula and method
Since 1959 the international mile has been exactly 1,609.344 metres, so one square mile is 1,609.344² = 2,589,988.110336 m², or 2.589988110336 km². Dividing by that number converts km² back to square miles, which is the same as multiplying by 0.386102.
An acre is defined as 1/640 of a square mile (4,046.8564224 m²), and a hectare is 10,000 m² (one hundredth of a km²). The converter first turns your value into square metres, then divides by the size of each target unit, so every output is consistent.
- sq mi
- Square mile, 1,609.344 m × 1,609.344 m
- km²
- Square kilometre, 1,000,000 m²
- ha
- Hectare, 10,000 m²
Worked examples
1 square mile in km²
One square mile is 1,609.344 m squared = 2,589,988 m², which is 2.59 km², 259 hectares and exactly 640 acres.
100 km² national park in square miles
100 ÷ 2.589988 = 38.61 square miles. In US land terms that is about 24,711 acres.
50-square-mile county in hectares
50 × 2.589988 = 129.5 km², which is 12,950 hectares. At 640 acres per square mile it is 32,000 acres.
1,000 acres of farmland in square miles
1,000 ÷ 640 = 1.5625 square miles, and 1,000 × 4,046.86 m² = 4.05 km².
Frequently asked questions
How many square kilometres are in a square mile?+
One square mile is exactly 2.589988110336 km², usually rounded to 2.59 km². Ten square miles is about 25.9 km².
How do I convert km² to square miles?+
Divide by 2.59, or multiply by 0.3861. For example, 500 km² × 0.3861 = 193.1 square miles.
How many acres are in a square mile?+
Exactly 640 acres. In the US public land survey a square mile is called a section, and a quarter section is 160 acres.
Is a square kilometre bigger than a square mile?+
No. A square mile is about 2.59 times larger than a square kilometre, because a mile (1.609 km) is longer than a kilometre.
What about US survey square miles?+
NIST declared the US survey foot obsolete on 1 January 2023. A survey square mile is about 2.589998 km², about 4 m² per km² (0.0004%) larger; it only matters when reading old land records.