Square Miles to Square Kilometers Converter
Enter an area in square miles to get the equivalent in square kilometers, or flip the direction and convert square kilometers back to square miles. The result updates as you type. A worked steps panel shows the exact arithmetic, and a reference table lists real-world landmark areas for quick comparison.
Formula
Worked example
To convert 5 square miles: 5 × 2.58998811 = 12.9499406 sq km. Reverse: 12.9499406 / 2.58998811 = 5 sq mi exactly. In acres: 5 × 640 = 3,200 acres. In hectares: 12.9499406 × 100 = 1,295 ha.
The sq mi to sq km conversion factor explained
One square mile is defined as a square with sides of exactly one international mile (1,609.344 metres). Squaring that length gives 1,609.344² = 2,589,988.11 square metres, which equals exactly 2.58998811 square kilometers. That factor is derived directly from the SI definition of the metre and the international yard-and-pound agreement of 1959, so it is exact to the digits shown and the same factor applies everywhere in the world. To go the other way, divide by 2.58998811 (or multiply by the reciprocal, 0.38610216 sq mi per sq km).
Square miles vs. square kilometers: which system uses which
Square miles are part of the imperial and US customary systems. They are the standard unit for land area in the United States, the United Kingdom (alongside hectares), and a handful of other countries. Square kilometers are an SI unit and are standard everywhere else. Most national statistics agencies publish land areas in sq km, as does the United Nations, the World Bank, and most scientific literature. The two units are directly proportional, so converting between them is a single multiplication or division. For very large areas such as countries, sq km produces more manageable numbers (Russia is about 6.6 million sq mi or 17.1 million sq km). For smaller urban areas, both units produce reasonable numbers: Manhattan is about 22.8 sq mi or 59.1 sq km.
Related area units: acres and hectares
Acres and hectares are the agricultural subdivision units within the imperial and metric systems respectively. One square mile equals exactly 640 acres, and one square kilometer equals exactly 100 hectares. Therefore 1 sq mi = 640 acres = 2.58998811 sq km = 258.998811 hectares. This calculator outputs all four values simultaneously so you do not need a second conversion step. If you are working with land parcels in the US, acres are the most common unit for plots smaller than a square mile; in Europe and most of the rest of the world, hectares fill that role.
How to read the conversion table and chart
The reference table above lists famous real-world areas in both units so you can anchor the numbers to something familiar. The chart shows how the output scales linearly from 10% to 10x your entered value, confirming that sq mi and sq km are in a constant ratio. There are no logarithmic or compound effects: double the area in square miles and you exactly double the area in square kilometers.
Real-world area landmarks in sq mi and sq km
| Place / feature | sq mi | sq km | Scale |
|---|---|---|---|
| Central Park, New York City | 1.317 | 3.41 | City park |
| Manhattan island, New York | 22.83 | 59.1 | Urban island |
| Paris (city proper) | 40.7 | 105.4 | Capital city |
| Los Angeles city | 502.7 | 1,301.9 | Major metro |
| Greater London | 606.8 | 1,572 | Capital region |
| Rhode Island (US state) | 1,212 | 3,139 | Small US state |
| Puerto Rico | 3,515 | 9,104 | US territory |
| Lake Ontario | 7,340 | 19,009 | Great Lake |
| New England (6 states) | 71,992 | 186,458 | US sub-region |
| Texas (US state) | 268,596 | 695,662 | Large US state |
| France | 248,573 | 643,801 | Country (Europe) |
| Alaska (US state) | 663,268 | 1,717,856 | Largest US state |
| Australia | 2,969,907 | 7,692,024 | Continent/country |
| Russia | 6,601,668 | 17,098,242 | World's largest country |
Approximate areas of well-known geographic features for quick mental comparison.
Frequently asked questions
How many square kilometers are in a square mile?
There are exactly 2.58998811 square kilometers in one square mile. This comes from the definition of a mile as 1,609.344 metres: 1,609.344 squared equals 2,589,988.11 square metres, or 2.58998811 sq km. The commonly rounded figure is 2.59 sq km per sq mi.
How do I convert square miles to square km manually?
Multiply the number of square miles by 2.58998811. For a quick mental estimate, multiplying by 2.59 is accurate to within 0.001%. Example: 10 sq mi × 2.59 = 25.9 sq km (exact: 25.8999 sq km).
How do I convert square km to square miles?
Divide the number of square kilometers by 2.58998811, or equivalently multiply by 0.38610216. Example: 100 sq km / 2.58998811 = 38.6102 sq mi.
Is a square mile bigger than a square kilometer?
Yes, one square mile is about 2.59 times larger than one square kilometer. Conversely, one square kilometer is about 0.386 square miles, so it is less than half a square mile.
How many acres are in a square mile?
There are exactly 640 acres in one square mile. Because one square mile equals 2.58998811 sq km, you can also say there are 258.998811 hectares in a square mile.
Why do the US and UK still use square miles for area?
The United States never officially adopted the metric system for everyday commercial use, so miles and square miles remain the legal and customary standard for land area. The United Kingdom officially adopted the metric system but still uses miles on road signs and in some land-related contexts due to historical convention and public familiarity. Both countries also use square kilometers in scientific and international contexts.
What is a quick way to estimate sq mi from sq km in my head?
Multiply sq km by 0.4 (instead of the exact 0.38610216) for a fast rough estimate. This overstates by about 3.6%, which is close enough for most conversational purposes. For sq mi to sq km, multiply by 2.6 instead of 2.59 - an error of about 0.4%.