Square Kilometers to Square Miles

A mile is 1.609344 km, so a square mile is 1.609344² = 2.589988 km². Put the other way, a square kilometer is a bit more than a third of a square mile. Manhattan's land area is about 59 km², or 22.7 sq mi; the land area of the whole Earth is close to 149 million km², roughly 57.5 million sq mi.

One square kilometer also equals 100 hectares or 247.1 acres, which makes it the natural unit once land outgrows a farm. If a figure is given in hectares, divide by 100 first; the hectares to acres page covers the smaller scale.

Density is people per unit of area, so converting it moves in the opposite direction from the area itself. Because a square mile is 2.59 times larger than a square kilometer, 1,000 people per km² equals 2,590 people per sq mi. Comparing a European city quoted per km² with an American one quoted per sq mi without converting makes the European one look 2.6 times less crowded than it really is.

The same rule applies to anything spread over land: forest per sq mi, wind turbines per km², or crop output per area. Multiply a per-km² figure by 2.59 to get per-sq-mi, and divide to go back.

Square miles are standard in the United States for states, counties and city limits, and the UK uses them informally. Almost every other country, along with the UN and most atlases, uses square kilometers. Wildfire reports in the US often give acres, which you can bring to square miles by dividing by 640. For every other area unit, the unit converter has the full list, including square feet to square meters for buildings.