Square Hectometer [hm²]
A square hectometer (hm²) is a unit of area equal to a square with sides 1 hectometer (100 meters) long.
1 hm² = 10,000 m² = 1 hectare (ha).
It is used to measure large areas like fields or forests, similar to hectares.
Acre (US Survey) [ac]
The acre (US survey) is a unit of area used mainly in the United States for land measurement, based on the US survey foot. It is slightly different from the international acre due to the foot definition.
1 US survey acre = 43,560 US survey square feet
1 US survey acre ≈ 4,046.87261 square meters
Slightly larger than the international acre by about 0.0005%.
It is commonly used in land surveying, real estate, and agriculture.