Construction & Home Improvement Formulas
A practical reference guide for estimating materials and costs on construction and home improvement projects. Bookmark this page for quick access.
Quick Navigation:
Concrete Estimation
Volume (cubic yards) = (Length × Width × Depth in feet) / 27
Steps:
- Measure area in feet (length × width)
- Convert depth to feet (inches / 12)
- Multiply: length × width × depth = cubic feet
- Divide by 27 to get cubic yards
- Add 5-10% for waste
Example:
A 20ft × 10ft patio, 4 inches deep:
20 × 10 × (4/12) = 66.67 cubic feet
66.67 / 27 = 2.47 cubic yards
With 10% waste: ~2.7 cubic yards
Tile & Flooring
Tiles Needed = Floor Area / Tile Area + Waste (10-15%)
Common Tile Sizes:
- 12" × 12" = 1 sq ft per tile
- 12" × 24" = 2 sq ft per tile
- 18" × 18" = 2.25 sq ft per tile
- 24" × 24" = 4 sq ft per tile
Example:
200 sq ft room with 12" × 12" tiles:
200 / 1 = 200 tiles
With 10% waste: 220 tiles
Paint Coverage
Gallons Needed = Total Wall Area / Coverage per Gallon
Coverage Rates:
- Interior paint: ~350 sq ft per gallon
- Exterior paint: ~300 sq ft per gallon
- Primer: ~300 sq ft per gallon
- Most projects: 2 coats recommended
Example:
Room: 12ft × 14ft, 8ft ceilings, 2 coats:
Wall area: 2(12 + 14) × 8 = 416 sq ft
Minus doors/windows: ~380 sq ft
2 coats: 760 sq ft / 350 = 2.2 gallons
Roofing Materials
Squares Needed = Roof Area (sq ft) / 100
Key Facts:
- 1 roofing square = 100 sq ft
- 3 bundles = 1 square (standard shingles)
- Add 10-15% for waste, hips, and valleys
- Steeper roofs need more material
Pitch Multiplier:
- 4/12 pitch: multiply area by 1.054
- 6/12 pitch: multiply area by 1.118
- 8/12 pitch: multiply area by 1.202
- 10/12 pitch: multiply area by 1.302
- 12/12 pitch: multiply area by 1.414
Lumber & Board Feet
Board Feet = (Thickness × Width × Length) / 144
All measurements in inches. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick (144 cubic inches).
Common Nominal vs Actual Sizes:
| Nominal | Actual |
|---|---|
| 2 × 4 | 1.5" × 3.5" |
| 2 × 6 | 1.5" × 5.5" |
| 2 × 8 | 1.5" × 7.25" |
| 2 × 10 | 1.5" × 9.25" |
| 2 × 12 | 1.5" × 11.25" |
Area & Volume Quick Reference
| Shape | Area Formula | Volume Formula |
|---|---|---|
| Rectangle | L × W | L × W × H |
| Triangle | ½ × B × H | — |
| Circle | π × r² | — |
| Cylinder | π × r² (end) | π × r² × H |