The one conversion to memorize
One acre equals 43,560 square feet. It also equals 4,840 square yards, 160 square rods or 10 square chains. Under time pressure candidates grab digit transpositions such as 43,650 or 45,360, and those wrong numbers are built into the distractors on purpose. A related trap is 5,280, which is the number of feet in a statute mile — a linear measure, not an area.
Converting a rectangle to acres
Multiply to get square feet, then divide by 43,560.
Worked example: a lot measures 300 feet by 726 feet. Area = 300 × 726 = 217,800 square feet. Then 217,800 ÷ 43,560 = 5.0 acres.
Watch the failure modes. Dividing by 87,120, twice the acre conversion, halves the answer to 2.5 acres. Dividing by a misremembered 45,360 or 43,650 gives about 4.6 acres. Doubling the area before converting gives 10.0 acres.
Fractional section problems
A section is 640 acres. For a call like "the N 1/2 of the SE 1/4 of the NW 1/4 of Section 12," multiply the denominators and divide once: 2 × 4 × 4 = 32, then 640 ÷ 32 = 20 acres.
Read it from the smallest division to the largest to check yourself: the NW 1/4 is 160 acres, the SE 1/4 of that is 40 acres, and the N 1/2 of that is 20 acres. Stopping one step early gives 40 acres; mishandling the N 1/2 gives 80; applying only the first fraction gives 160.
Measuring living area
Living area counts only finished heated space, measured from exterior dimensions. A house of 48 × 28 plus a heated addition of 12 × 16 gives 1,344 + 192 = 1,536 square feet.
An unheated 484 square foot garage is excluded — adding it gives 2,020. Adding the garage and a 160 square foot open porch gives 2,180, the classic double error. Omitting the heated addition gives 1,344.