The hectare and the acre are the two units in which serious land — farms, estates, government allocations — is measured worldwide. The hectare is metric: exactly 10,000 square meters, the area of a 100 m × 100 m square. The acre is imperial: exactly 43,560 square feet. One hectare equals about 2.47 acres, and one acre is about 0.405 hectares.
In India and Nepal both appear constantly: official digitized records and agricultural statistics use hectares, while older deeds, real-estate listings, and everyday speech lean on acres (and regional units like the bigha). A useful mental shortcut is "hectares × 2.5, minus a little" — 4 hectares ≈ 10 acres is accurate to within about 1%.