Roofing Calculator
Estimate the roof area, number of squares and bundles of shingles needed for a gable or hip roof.
How to use the Roofing Calculator
- Enter the building length and pick its unit.
- Enter the building width and pick its unit.
- Enter the eave overhang and pick its unit.
- Enter the roof pitch (rise per 12 in of run).
- Enter the waste allowance – 10% for simple gable roofs, 15% for hip roofs and valleys.
- Choose the bundles per square.
- Enter the installed price per square.
- Press Calculate. The result updates automatically as you type, and you can switch the result unit at any time.
About the Roofing Calculator
Roofers price and order materials by the square, so converting your roof to squares is the first step toward a quote. You can measure the footprint on the ground, add the overhang on every side, and let the pitch multiplier account for the slope, without climbing onto the roof.
Add 10% waste for a simple gable, 15% or more for hip roofs, dormers and valleys. The estimate does not include ridge cap, starter strip, drip edge or flashing, which are ordered by linear feet. Roofs with mixed pitches should be calculated one section at a time.
Formula
Pitch multiplier = √(1 + (pitch ÷ 12)²)
Roof area = (Length + 2 × overhang) × (Width + 2 × overhang) × multiplier
Squares = Roof area ÷ 100 × (1 + waste %)
One roofing square covers 100 sq ft. Most asphalt shingles come 3 bundles per square. For any roof whose planes all share the same pitch, gable or hip, the sloped area equals the footprint (including overhangs) times the pitch multiplier.
Example calculation
Using the default values:
- Building length = 40 ft
- Building width = 30 ft
- Eave overhang = 12 in
- Roof pitch (rise per 12 in of run) = 6 in 12
- Waste allowance = 10%
- Bundles per square = 3 (most 3-tab and architectural)
the calculator returns:
- Roof area: 1,502.6 ft²
- Squares to order (incl. waste): 16.53
- Shingle bundles: 50 bundles
- Underlayment rolls (#15 felt, ~400 sq ft): 4 rolls
- Pitch multiplier: 1.118
Frequently asked questions
How many square feet is a roofing square?
One roofing square is 100 square feet (10 × 10 ft) of roof surface.
How many bundles of shingles cover a square?
Most 3-tab and architectural shingles take 3 bundles per square, so each bundle covers about 33.3 sq ft. Some heavy designer shingles need 4 or 5.
How do I find my roof pitch?
Hold a level horizontally against the roof or a rafter, measure 12 inches along it, and measure straight up to the roof surface. That vertical distance is the rise per 12, e.g. 6/12.
Last updated: · Category: Construction calculators