Roofing Calculator — Squares & Shingle Bundles
Estimate a roof without climbing a ladder. Enter the home's footprint, overhang and roof pitch to get the roof area, roofing squares, shingle bundles, underlayment, drip edge and ridge cap.
Roof area
How to estimate roofing materials
- Measure the outside length and width of the building and the eave overhang.
- Choose the roof pitch: the rise in inches per 12 inches of run (a 6/12 roof rises 6 inches per foot).
- Choose gable or hip and a waste allowance: 10% for simple gables, 15% or more for hips and complex roofs.
How roof area is calculated
The roof covers the footprint plus the overhang on every side, stretched by the slope. The pitch factor, √(1 + (pitch ÷ 12)²), converts flat area to sloped area: a 6/12 roof has about 11.8% more surface than its footprint, and a 12/12 roof about 41% more. For a simple hip roof with equal pitches, the same factor applies to the whole footprint.
Roofing is sold by the square, 100 square feet of roof. Standard architectural shingles come three bundles to a square. Add waste for cuts at hips, valleys and edges, plus starter strips and ridge cap. Dormers, valleys and skylights add complexity; measure those sections separately or raise the waste allowance.
Steep roofs (above about 8/12) need extra safety equipment and usually cost more to install. Check local code for underlayment and ice-barrier requirements, and confirm quantities with your supplier before ordering.
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Frequently asked questions
How many bundles of shingles are in a square?
Three for most architectural and 3-tab shingles. Some heavy designer shingles use four or five.
How do I find my roof pitch?
Measure the rise over a 12-inch level from the roof surface, or use a pitch gauge or phone app.
How much waste should I add?
About 10% for simple gable roofs and 15% or more for hip roofs, valleys and dormers.
How many nails per square?
About 320 nails per square for 4 nails per shingle, more (about 480) where high-wind 6-nail patterns are required.