Cheat Sheet · 01
americasmarket.comMeasurements & Conversions
CA Contractor Exam · the magic numbers
Decimal Feet ↔ Inches
Trick: decimal ft × 12 = inches. The engineer's tape is in tenths of a foot, not inches.
0.1 ft1.2"0.6 ft7.2" 0.2 ft2.4"0.7 ft8.4" 0.25 ft3"0.75 ft9" 0.3 ft3.6"0.8 ft9.6" 0.4 ft4.8"0.9 ft10.8" 0.5 ft6"1.0 ft12"
Lumber: Nominal vs Actual
2×4 → 1½ × 3½2×10 → 1½ × 9¼ 2×6 → 1½ × 5½2×12 → 1½ × 11¼ 2×8 → 1½ × 7¼4×4 → 3½ × 3½ 1×4 → ¾ × 3½4×6 → 3½ × 5½
Board foot = T(in) × W(in) × L(ft) ÷ 12
Area & Volume
- 1 sq ft = 144 sq in · 1 sq yd = 9 sq ft
- 1 acre = 43,560 sq ft = 4,840 sq yd
- 1 cu ft = 1,728 cu in · 1 cu yd = 27 cu ft
- 1 cu ft = 7.48 gal · 1 gal = 231 cu in
- Concrete (yd³) = L′ × W′ × H′ ÷ 27
Scales on the Plans
Engineer's
1" = 10' · 20' · 30'
40' · 50' · 60'
site / civil
Architect's
¼" = 1' (most plans)
⅛" · ½" · ¾" · 1"
building / detail
Roof Pitch (rise/12)
3/12≈14°8/12≈34° 4/12≈18°9/12≈37° 5/12≈23°10/12≈40° 6/12≈27°12/1245°
Rafter length = run × √(1 + (rise/run)²). 6/12 multiplier ≈ 1.118.
Always Memorize
- 1 mile = 5,280 ft
- 1 yd = 3 ft
- 1 ft = 12 in
- 1 m ≈ 3.28 ft
- 1 lb = 16 oz
- 1 ton = 2,000 lb