Roofing Calculator
Turn a building footprint and roof pitch into roof area, roofing squares, shingle bundles, underlayment rolls, ridge cap and starter strip with waste added.
The slope factor is √(rise² + run²) ÷ run with run = 12, so a 6/12 pitch multiplies the ground footprint by 1.1180. One roofing square is 100 sq ft (9.29 m²). A 10% waste allowance is applied before bundles are counted. Dormers, valleys, overhangs and multiple roof planes are not modelled — measure each plane separately for anything but a simple gable. Estimates only; roofing is a fall risk, so use a qualified contractor.
What is the Roofing Calculator?
The ByteTools Roofing Calculator converts the footprint of a building and its pitch into the sloped roof area, then into materials.
- Exact pitch multiplier and roof angle in degrees
- Roof area in squares, square feet and square metres
- Shingle bundles at your bundles-per-square figure
- Underlayment rolls for synthetic, #15 and #30 felt
- Ridge cap bundles and starter strip rolls
- Imperial and metric, computed entirely in your browser
How to use the Roofing Calculator
- 1
Choose imperial or metric and enter the building footprint length and width.
- 2
Enter the roof pitch as rise per 12 of run — 6 means a 6/12 pitch.
- 3
Set the waste allowance: 10% for a simple gable, 15% for a hip roof or many valleys.
- 4
Pick the underlayment roll size and enter your ridge, hip and eave lengths.
- 5
Read the roof area in squares, and the bundles and rolls you need.
About the Roofing Calculator
The ByteTools Roofing Calculator converts the footprint of a building and its pitch into the sloped roof area, then into materials. It applies the standard slope factor — the square root of rise squared plus run squared, divided by the run — so a 6/12 pitch multiplies your ground area by 1.1180, and reports the result in squares, square feet and square metres.
From that area it counts shingle bundles at three per square, underlayment rolls at the roll size you select, ridge cap bundles from your ridge and hip length, and starter strip from the eave length. A waste allowance covers cuts at valleys, rakes and penetrations.
All of it happens in your browser with nothing uploaded. This models a simple roof plane — dormers, valleys and multiple sections need measuring separately — and roofing work carries a genuine fall risk, so use a qualified contractor for anything you cannot safely reach.
Frequently asked questions
How do I calculate roof area from the footprint?
Multiply the ground footprint by the slope factor for your pitch. The slope factor is √(rise² + run²) ÷ run with the run fixed at 12, so a 6/12 pitch gives √(36 + 144) ÷ 12 = 1.1180. A 1,200 sq ft footprint at 6/12 is therefore about 1,342 sq ft of roof.
How many bundles of shingles are in a square?
Three bundles cover one roofing square, which is 100 square feet or 9.29 square metres. That holds for standard three-tab and most architectural shingles; heavier premium and designer shingles can take four or five bundles per square, so check the wrapper.
How much waste should I add for roofing?
Ten percent is the usual allowance for a simple gable roof. Hip roofs, roofs with several valleys, and anything with dormers or complicated penetrations run to 15% or more because every diagonal cut wastes part of a shingle.
What is a roofing square?
A square is 100 square feet of roof surface — the unit roofers price and order in. It is a measure of the sloped surface, not the ground footprint, which is why the pitch multiplier has to be applied first.
Does this calculator handle hip roofs and dormers?
Not directly. It models a single roof plane geometry from a rectangular footprint. For hips, dormers, valleys and multi-section roofs, measure each plane separately and add the results, and raise the waste allowance to reflect the extra cuts.
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