Acres are measured in square feet, and there are 43,560 square feet in 1 acre. If the acre of land is perfectly square, each side will be just under 209 feet long.
To calculate square footage in order to determine if a square piece of land is 1 or more acres, measure two sides and multiply the numbers together. The product of the multiplied numbers is the square footage. Compare the number calculated to 43,560 to determine if the piece of land is larger, smaller or equal to 1 acre. If the land is unusually shaped, the calculations become more complicated, and measuring each side is necessary.