How to estimate roofing materials

This estimator is for a simple, symmetrical gable roof. It starts with the building footprint, extends the plan dimensions by the selected overhang and adjusts the plan area for roof pitch. It then converts the surface into roofing squares and estimates shingle bundles using the coverage you enter.

Roof area formula

Pitch multiplier = √(1 + (rise ÷ 12)²)

Adjusted plan area = (building length + 2 × overhang) × (building width + 2 × overhang)

Roof surface area = adjusted plan area × pitch multiplier

One US roofing square equals 100 square feet. The calculator adds your waste percentage before converting surface area to bundles.

Worked example

For a 40 ft × 30 ft footprint, 6:12 pitch and 12-inch overhang on each edge, the pitch multiplier is √(1 + 0.5²), or about 1.118. The adjusted plan dimensions are 42 ft × 32 ft. The resulting roof surface is about 1,503 square feet before waste. The final shingle bundle count depends on the bundle coverage printed on the product packaging.

Important limitations

• This is a simple gable-roof estimate, not a detailed roof plan. It does not model hips, valleys, dormers, intersecting planes, curved roofs or complex flashing details.
• It estimates shingle bundles only. Underlayment, starter strips, ridge caps, drip edge, nails, flashing and ventilation are not included.
• Pitch is entered as rise per 12 inches of horizontal run. Confirm the roof pitch and all dimensions from plans or a qualified roofer.
• Coverage differs by shingle type and exposure. Use the manufacturer’s package coverage, not an assumed universal bundle size.

Frequently asked questions

Related estimators: Flooring Calculator · Paint Coverage Calculator · Tile Calculator.

This tool is for preliminary material planning only. Have roof geometry, safety requirements and the final material take-off checked by a qualified roofing professional.