One acre equals exactly 43,560 square feet

For a rectangular parcel, multiply frontage by depth when both measurements are in feet. A lot measuring 150 feet by 290.4 feet contains 43,560 square feet, or one acre. A 100-by-200-foot lot contains 20,000 square feet, so divide by 43,560 to get about 0.459 acre.

For a triangle, use one-half times base times height. For an irregular tract, the question may divide the land into familiar shapes. Do not multiply mismatched units such as feet by yards without converting first.

A nominal section contains 640 acres. One-half is 320, one-quarter is 160, one-eighth is 80, and one-sixteenth is 40. A quarter-quarter section is therefore a nominal 40 acres because 640 times one-quarter times one-quarter equals 40.

Actual Public Land Survey System parcels can vary because original corners and lines, convergence, correction practices, and government lots control the surveyed land. Use the nominal values for a standard exam calculation unless the problem provides actual acreage or irregular-lot facts.

An acre can be a square, rectangle, triangle, or irregular polygon. If it is a perfect square, each side is approximately 208.71 feet because that is the square root of 43,560. That approximation does not mean every acre measures 208.71 feet on each side.

Frontage alone cannot determine acreage. A parcel with 100 feet of road frontage could contain less than an acre or many acres depending on depth and shape. The complete dimensions or a stated area are required.