The hectare is a unit of area and is a non-SI but metric unit with the symbol ha.
It represents the area equal to that of a square with edges 100m long (ie 1hm² or 10,000m²). This is the equivalent to about 2.47 acres.
Its size is down to its use primary use; that for measuring the size of land.
The square inch is a unit of area and is an imperial unit with the symbol in².
One square inch is equal in area to a square with edges one inch in length.
The square inch is a common unit of measurement in the UK and US.