Roofing Calculator
Turn your house footprint and roof pitch into roof area, roofing squares and the number of shingle bundles to order.
- Roof pitch
- Squares & bundles
- Overhang & waste
- Underlayment
Roofing squares and shingle bundles
Fill in the boxes. The answer appears as you type.
How is roof area calculated?
Roofing is measured in squares: 100 square feet of roof. To estimate it, take the house footprint including the eaves overhang and multiply by a pitch factor, because a sloped roof has more area than the ground it covers. A 6/12 pitch (6 inches of rise per 12 inches of run) has a multiplier of 1.118. Add 10–15% for waste on cuts, hips and valleys, divide by 100 for squares and multiply by 3 for bundles of standard shingles.
How to use Roofing Calculator
- Measure the house length and width (outside walls).
- Enter the roof pitch as inches of rise per 12 inches and the overhang in inches.
- Set waste: 10% for simple gable roofs, 15% for hips and valleys.
- Read the squares, bundles and underlayment rolls.
Roof pitch multipliers
- 4/12 → 1.054 · 6/12 → 1.118 · 8/12 → 1.202 · 10/12 → 1.302 · 12/12 → 1.414.
- One square = 100 sq ft = 3 bundles of standard asphalt shingles.
- Add 10% waste for gable roofs, 15% or more for hip roofs and valleys.
- Synthetic underlayment rolls often cover about 4 squares (400 sq ft).
Why use this roofing calculator
- Answers as you typeNo Calculate button. Change any number and every result updates instantly.
- Shows the workingEach answer has a plain-English sentence, the steps and a formula for Excel or Google Sheets.
- Buy the right amountResults are in the units stores sell (gallons, squares, bundles, BTU sizes), with sensible allowances built in.
- PrivateYour numbers are calculated on your device and never sent anywhere.
Common uses
- Re-roofing quotes. Check contractor estimates.
- DIY shed and garage roofs. Order the right number of bundles.
- Insurance claims. Estimate roof size quickly.
- Budgeting. Price shingles and underlayment.
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Example: a 40 × 30 ft house with a 6/12 roof
Footprint with 12 in overhang: 42 × 32 = 1,344 sq ft × 1.118 = 1,503 sq ft roof. +10% waste = 1,653 sq ft → 16.5 squares → 50 bundles.
What to expect from the result
This assumes one uniform pitch over a simple footprint. Dormers, multiple pitches and complex rooflines need each section measured separately. Always confirm with a roofer before ordering.
Roofing Calculator questions
How many bundles of shingles do I need?
Three bundles per roofing square (100 sq ft) for standard asphalt shingles. A 16.5-square roof needs 50 bundles.
What is a roofing square?
100 square feet of roof surface, the unit roofers use to price and order materials.
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches horizontally with a level and tape, or use the pitch on your house plans.
How much waste should I allow?
About 10% for simple gable roofs and 15–20% for hip roofs and roofs with valleys or dormers.
Does the overhang count?
Yes. Eaves and rakes are roofed too, so include the overhang on every side.