Unit Conversions
Most math errors on the exam are conversion errors — mixing feet with inches, or square with cubic.
÷ 9 sq ft → sq yd · ÷ 27 cu ft → cu yd · inches ÷ 12 → feet · 1 acre = 43,560 sq ft · 1 yd = 3 ft · 1 ton = 2,000 lb · 1 cu ft ≈ 7.48 gal · 80-lb bag ≈ 0.6 cu ft (~45 bags per cu yd).
The big ones
- Area: square feet ÷ 9 = square yards (a yard is 3 ft, so a square yard is 9 sq ft).
- Volume: cubic feet ÷ 27 = cubic yards (3 × 3 × 3).
- Thickness: always convert inches to feet (÷ 12) before computing a volume — 4 in = 0.33 ft, 6 in = 0.5 ft.
Mixing units is the trap: a slab thickness given in inches must become feet before you multiply length × width × thickness.
Practice: Unit Conversions
Frequently asked
What are the two most important construction conversions?
How do you turn inches into feet for a calculation?
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