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Square mile to square kilometer — two-way area converter
One square mile is 2.58999 square kilometers, 640 acres, and 258.999 hectares. Enter an area in either box and the other updates.
★ EVERYDAY · CONVERTERS · AREA
Square Mile to Square Kilometer Converter (mi² to km²)
1 square mile is 2.58999 square kilometers — 2.59 km², 640 acres, and 258.999 hectares. Convert square miles to square kilometers, acres, and hectares, or square kilometers back to square miles, in either direction.
How the square mile conversion works
A square mile is the area of a square one mile on each side, and a square kilometer is the area of a square one kilometer on each side. One mile is exactly 1.609344 kilometers, so one square mile is 1.609344² square kilometers, which is 2.589988 — rounded to 2.58999 km² on this page. Going the other way, one square kilometer is 1 / 2.58999 = 0.386102 square miles. A square mile is also exactly 640 acres, because an acre is 1/640 of a square mile, and 640 acres is 258.999 hectares, because one acre is 0.404686 hectares.
At the defaults — 1 square mile — the conversion is 1 × 2.58999 = 2.59 km², and the same area is 1 × 640 = 640 acres and 640 × 0.404686 = 258.999 hectares. The converter works both ways: type square miles and it gives square kilometers, acres, and hectares; type square kilometers and it gives square miles back. Both boxes stay in sync, so you can convert in whichever direction you are thinking.
| Square miles | Square kilometers | Acres | Hectares |
|---|---|---|---|
| 0.1 | 0.26 | 64 | 25.900 |
| 0.5 | 1.29 | 320 | 129.500 |
| 1 | 2.59 | 640 | 258.999 |
| 2 | 5.18 | 1,280 | 517.998 |
| 5 | 12.95 | 3,200 | 1,294.995 |
| 10 | 25.90 | 6,400 | 2,589.990 |
| 25 | 64.75 | 16,000 | 6,474.976 |
| 50 | 129.50 | 32,000 | 12,949.952 |
| 100 | 259.00 | 64,000 | 25,899.904 |
| Square kilometers | Square miles | Acres |
|---|---|---|
| 1 | 0.39 | 247.105 |
| 5 | 1.93 | 1,235.526 |
| 10 | 3.86 | 2,471.053 |
| 25 | 9.65 | 6,177.632 |
| 50 | 19.31 | 12,355.264 |
| 100 | 38.61 | 24,710.528 |
The worked example, line by line
Setup: area 1 square mile.
Line 1 — the conversion factor. 1 mile = 1.609344 km, so 1 mi² = 1.609344² km² = 2.58999 km².
Line 2 — square kilometers. 1 × 2.58999 = 2.59 km².
Line 3 — acres. 1 × 640 = 640 acres, exactly.
Line 4 — hectares. 640 × 0.404686 = 258.999 hectares.
Line 5 — the reverse. 1 km² = 1 / 2.58999 = 0.386102 mi², and 0.386102 × 640 = 247.105 acres.
Every branch, checked
5 square miles: 5 × 2.58999 = 12.95 km², 5 × 640 = 3,200 acres, and 3,200 × 0.404686 = 1,294.995 hectares.
100 square miles: 100 × 2.58999 = 259.00 km², 100 × 640 = 64,000 acres, and 64,000 × 0.404686 = 25,899.904 hectares.
0.5 square miles: 0.5 × 2.58999 = 1.29 km², 0.5 × 640 = 320 acres, and 320 × 0.404686 = 129.500 hectares.
Reverse — 10 km²: 10 × 0.386102 = 3.86 square miles, and 3.86 × 640 = 2,471.05 acres.
Reverse — 100 km²: 100 × 0.386102 = 38.61 square miles, and 38.61 × 640 = 24,710.5 acres.
Reverse — 1 km²: 1 × 0.386102 = 0.39 square miles, and 0.39 × 640 = 247.105 acres.
What the defaults assume
The conversion uses the exact international mile, 1 mile = 1.609344 kilometers, so 1 mi² = 2.589988110336 km², shown as 2.58999 on this page, and the reverse factor 0.386102 is 1 / 2.58999 rounded to six decimals. Acres are exact: 1 square mile is exactly 640 acres by definition. Hectares use 1 acre = 0.40468564224 hectares, so 1 square mile is 258.9988110336 hectares, shown as 258.999. Rounding convention: square kilometers and square miles to two decimals, acres to whole numbers except where shown, hectares to three decimals, all computed from unrounded values.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Square kilometers | mi² × 2.58999 | 2.59 km² for 1 square mile. |
| Acres | mi² × 640 | 640 acres for 1 square mile, exactly. |
| Hectares | acres × 0.404686 | 258.999 ha for 1 square mile. |
| Square miles (reverse) | km² × 0.386102 | 1 mi² for 2.58999 km². |
| 5 square miles | 5 × 2.58999 | 12.95 km²; 3,200 acres; 1,294.995 ha. |
| 100 square miles | 100 × 2.58999 | 259.00 km²; 64,000 acres; 25,899.904 ha. |
| 0.5 square miles | 0.5 × 2.58999 | 1.29 km²; 320 acres; 129.500 ha. |
| 10 km² | 10 × 0.386102 | 3.86 mi²; 2,471.05 acres. |
| 100 km² | 100 × 0.386102 | 38.61 mi²; 24,710.5 acres. |
| Reverse: 1 km² | 1 × 0.386102 | 0.39 mi²; 247.105 acres. |
Who uses this
- The hiker reading a trail map: sees a park listed as 25 square miles and learns it is 64.75 km² — so the metric map and the imperial guidebook are describing the same place.
- The student comparing city sizes: reads that a city covers 100 square miles and learns it is 259.00 km² — so it can be compared directly with a European city measured in square kilometers.
- The land buyer checking acreage: is offered 5 square miles of land and learns it is 3,200 acres and 1,294.995 hectares — so the listing can be checked against county records in any unit.
- The researcher working in metric: has a study area of 10 km² and learns it is 3.86 square miles — so the paper can quote the area in the units its American readers expect.
Accuracy & limitations
The math is exact for the numbers you enter: the factor 2.58999 is 1.609344² rounded to five decimals, the reverse factor 0.386102 is its reciprocal rounded to six decimals, and 640 acres per square mile is exact by definition. The only error is rounding: using 2.58999 instead of the full 2.589988110336 changes the result by less than 0.0005% — about 5 square meters on a square mile — which is far below what any map or listing can measure. For land-survey work that needs the last decimal, use the full factor 2.589988110336. Read the kilometers to miles converter for the matching length conversion.
Cite this calculatorBright Side Kit. “Square Mile to Square Kilometer Converter (mi² to km²)” brightoolbox.com, 2026. Method: 1 mile = 1.609344 km exactly, so 1 mi² = 1.609344² = 2.58999 km²; 1 km² = 0.386102 mi²; 1 mi² = 640 acres exactly; 1 acre = 0.404686 ha. Defaults: 1 mi² → 2.59 km², 640 acres, 258.999 ha; 5 mi² → 12.95 km², 3,200 acres, 1,294.995 ha; 100 mi² → 259.00 km², 64,000 acres, 25,899.904 ha; 0.5 mi² → 1.29 km², 320 acres, 129.500 ha; 10 km² → 3.86 mi², 2,471.05 acres; 100 km² → 38.61 mi², 24,710.5 acres; 1 km² → 0.39 mi², 247.105 acres. No external data needed — all math is from the inputs.
Bright Side Kit. "Square Mile to Square Kilometer Converter (mi² to km²)" https://brightoolbox.com/square-mile-to-square-kilometer/ Accessed October 24, 2026.Frequently asked questions
How many square kilometers are in one square mile?
2.58999 square kilometers. One mile is 1.609344 kilometers, and squaring it gives 1.609344² = 2.58999 km². So 1 square mile is 2.59 km², 5 square miles is 12.95 km², and 100 square miles is 259.00 km².
How many square miles are in one square kilometer?
0.386102 square miles. It is the reciprocal of 2.58999: 1 / 2.58999 = 0.386102. So 10 km² is 3.86 square miles and 100 km² is 38.61 square miles.
How many acres are in a square mile?
640 acres, exactly. An acre is defined as 1/640 of a square mile, so 1 square mile is 640 acres, 5 square miles is 3,200 acres, and 100 square miles is 64,000 acres.
How many hectares are in a square mile?
258.999 hectares. One acre is 0.404686 hectares, and 640 × 0.404686 = 258.999. A square mile is just under 259 hectares.
Why is the factor 2.58999 and not a round number?
Because it is the square of 1.609344. The mile is defined as exactly 1.609344 kilometers, and 1.609344 × 1.609344 = 2.589988110336. Area factors are the square of length factors, so they are never round.
Can I convert square kilometers back to square miles here?
Yes — the converter works both ways. Type a number in either box and the other updates: 10 km² becomes 3.86 square miles, and 1 km² becomes 0.39 square miles.
What is bigger, a square mile or a square kilometer?
A square mile is bigger, by about 2.6 times. One square mile is 2.59 square kilometers, while one square kilometer is only 0.39 square miles. A square mile is roughly the size of 484 American football fields.
How accurate is this converter?
Accurate to within 0.0005%. The factor 2.58999 is 1.609344² rounded to five decimals, so the error on a whole square mile is about 5 square meters. Acres are exact, and hectares use 1 acre = 0.404686 hectares.