What are Square Millimeters?
A square millimeter is the area of a square one millimeter on each side, so there are 100 in a square centimeter and 1,000,000 in a square meter. Electrical cable is sized by cross-section in them – 1.5mm² and 2.5mm² are common.
What are Hectares?
A hectare is 10,000 square meters, or about 2.47 acres. It is the usual metric unit for land, so farms, parks and forests are measured in hectares.
A hectare is the area of a square 100 meters on each side. The name is 'hecto-' plus are, an are being 100 square meters, so a hectare is 100 ares.