What waste percentage should I use for roofing?

For simple gable roofs, 10% waste is common. For hips, valleys, lots of penetrations, or complex layouts, 15% or more may be needed.

What is a roofing square?

A roofing square is 100 square feet of roof surface area. Shingles are often priced and estimated using squares and bundles.

Can I use custom roof area instead of length/width and pitch?

Yes. If you already have the sloped roof area from plans or a measurement, use Custom Roof Area to estimate materials directly.

Roofing Calculator (Shingles or Sheets)

Roofing Calculator

Estimate roof surface area and materials. Use footprint + pitch to get sloped area, add waste for cuts and complexity, then convert to bundles (shingles) or sheets/panels (by coverage).

Roofing Calculator

Estimate roof area and materials (asphalt shingles or metal sheets) with waste allowance

Material

Input method

Roof length (footprint)

Roof width (footprint)

Roof pitch angle

Waste allowance

Results

Enter dimensions above to calculate

Formulas used

Roofing estimates start with area, then adjust for pitch and waste. The calculator uses common trade conventions like squares for shingles.

1. Footprint Area

Formula:

Plan Area = Length × Width

Start with the roof footprint (horizontal projection). For most simple roofs, this is the building length times building width (including overhangs if you want a closer estimate).

2. Convert Pitch to Slope Factor

Formula:

Slope Factor = √(1 + (Rise/Run)²) (or 1/cos(θ))

Pitch increases the surface area compared to the footprint. A steeper roof means more material due to longer rafter lengths.

3. Roof Surface Area

Formula:

Roof Area (sloped) = Plan Area × Slope Factor

For simple gable or shed roofs, total sloped area is footprint area multiplied by the slope factor.

4. Waste Allowance

Formula:

Order Area = Roof Area × (1 + Waste%)

Waste covers cuts, valleys/hips, starter courses, and mistakes. 10% is typical for simple roofs; 15%+ for complex roofs.

5. Convert Area to Materials

Formula:

Shingles: Squares = ft²/100 | Bundles ≈ Squares × 3

Asphalt shingles are often sold by the square (100 ft²) and by bundles. Metal panels/sheets are typically estimated by coverage per sheet/panel.

Example

Simple gable roof: 10 m × 8 m footprint, 30° pitch, 10% waste.

Plan area = 10 × 8 = 80.0 m²
Slope factor = 1/cos(30°) ≈ 1.1547
Roof area = 80.0 × 1.1547 ≈ 92.38 m²
Order area = 92.38 × 1.10 ≈ 101.62 m²
Squares ≈ (101.62 × 10.7639) ÷ 100 ≈ 10.94, Bundles ≈ ceil(10.94 × 3) = 33

Frequently Asked Questions

What waste percentage should I use for roofing?: For simple gable roofs, 10% waste is common. For hips, valleys, lots of penetrations, or complex layouts, 15% or more may be needed.
What is a roofing square?: A roofing square is 100 square feet of roof surface area. Shingles are often priced and estimated using squares and bundles.
Can I use custom roof area instead of length/width and pitch?: Yes. If you already have the sloped roof area from plans or a measurement, use Custom Roof Area to estimate materials directly.