Convert square millimeter to hectare

Common mistakes

• A hectare is 10,000 m², a 100 × 100 m square, and one square kilometer holds 100 hectares. News stories about wildfires and land plots often mix the two up. Rule of thumb: a football pitch is roughly 0.7 hectares.
• An acre is about 4,047 m², which is roughly 0.405 hectares, not the other way around. One hectare holds about 2.47 acres. Buying property abroad: multiply acres by 0.405 to get hectares.
• The Swedish tunnland, the area one barrel of seed could sow, is about 4,936 m², roughly half a hectare. Older property records are often misread as full hectares. Working rule: two tunnland ≈ one hectare.
• For areas the length factor must be squared, using it directly is the classic trap. 1 km is 1,000 m, but 1 km² is 1,000,000 m², and 1 m² is 10,000 cm². The rule: convert the length unit, then square the factor.