Square kilometre (U.S. spelling: square kilometer), symbol km 2 , is a decimal multiple of the SI unit of surface area, the square metre, one of the SI derived units. 1 km 2 is equal to:

• 1,000,000 m 2
• 100 ha (hectare)

Conversely:

• 1 m 2 = 0.000 001 (10 −6 ) km 2
• 1 hectare = 0.01 (10 −2 ) km 2
• 1 square mile = 2.589 988 km 2
• 1 acre = 0.004 047 km 2 , 40.47 ha or 4047 m 2

Note: "km 2 " means (km) 2 , square kilometre or kilometre squared, and not k(m 2 ), kilo–square metre. For example, 3 km 2 is equal to 3 × (1,000 m) 2 = 3,000,000 m 2 , not 3,000 m 2 .

== Comparative order

The 10 6 m 2 orders of magnitude page gives comparisons with geographic areas.

A hectare (10 4 m 2 ) is less than a square kilometer which is less than a square megametre (10 12 m 2 ).