The area units ‘square mile’ and ‘hectare’ are used to measure land, both are used, but their size and history are very different.

Square Mile:
The area is commonly referred to as a square mile in the imperial system and is used in most countries based on the imperial system. It is the square mileage of a square one mile long with each side a mile (1 mile = 1.60934 kilometers). Large land areas are frequently stated in the sense of cities, countries states, etc. in square miles.
1 square mile = 2.58999 square kilometers or 640 acres.

1 square mile is:

25,899,881,103.36 square centimetres
2,589,988.110336 square metres
258.9988110336 hectares
2.589988110336 square kilometres
640 acres
4,014,489,600 square inches
27,878,400 square feet
3,097,600 square yards

Hectare:
The metric unit used of hectare is a unit of area used also globally, most commonly in agriculture and forestry. An area of 10 thousand square meters is equal to the side of the square which is 100 metres long. Fields, farms, and forests are commonly measured on hectares.
1 hectare = 0.01 square kilometres = 2.47105 acres.