Roofing Shingle Calculator
From the horizontal footprint and the pitch, this tool computes the true sloped area, expresses it in roofing squares, and counts shingle bundles — with waste applied before the round-up and a cost line at your bundle price.
Footprint and pitch
Example: a 1,500 sq ft footprint at 6/12 pitch with 10% waste → 56 bundles.
Bundle counts are an ordering estimate — roof structure, ventilation, underlayment choices, code compliance, and permits require a licensed roofing professional.
Pitch stretches the footprint
The slope factor is √(1 + (rise ÷ 12)²) — pure Pythagoras, computed live rather than
looked up. The worked roof: 1,500 sq ft of footprint at 6/12 carries a factor of 1.118, so the shingles actually cover 1,677.05 sq ft — 16.77 squares. Waste lifts that to 18.45 squares, and at 3 bundles per square the order is 56 bundles.
Skipping the factor and ordering from the footprint alone would have left the last 177.05 sq ft bare.
Computed factors for common pitches
| Pitch (rise/12) | Slope factor | 1,000 sq ft footprint becomes |
|---|---|---|
| 2/12 | 1.014 | 1,013.79 sq ft |
| 4/12 | 1.054 | 1,054.09 sq ft |
| 6/12 | 1.118 | 1,118.03 sq ft |
| 8/12 | 1.202 | 1,201.85 sq ft |
| 10/12 | 1.302 | 1,301.71 sq ft |
| 12/12 | 1.414 | 1,414.21 sq ft |
Every factor in the table is generated at build time by the same pitchFactor
function the form calls — there is no hardcoded table to drift out of date.
Frequently asked questions
What is a roofing square, and why bundles?
A square is 100 sq ft of roof — the industry’s unit of account. Asphalt shingles ship in bundles sized so that a set number covers one square: 3 bundles for standard three-tab and common architectural lines per the manufacturers’ spec sheets, 4 to 6 for some premium products. You buy bundles, so the tool ends there.
How do I find my roof’s rise?
Measure how many inches the roof climbs over 12 inches of horizontal run — from an attic rafter with a level and tape, or from the gable end. A “6/12 roof” rises 6 inches per foot. Enter just the rise number; the tool does the trigonometry.
Why is the roof area bigger than my house’s footprint?
Because shingles lie on the slope, not on the floor plan. The slope stretches every horizontal foot by √(1 + (rise/12)²) — about 12% longer at 6/12 and 41% at 12/12. Estimating from the footprint without the factor is the classic way to run short.
When should I raise the waste percentage?
The 10% default suits simple gable roofs. Hips, valleys, dormers, and chimneys all generate cut shingles, so complex roofs conventionally get 15% or more. Starter strips and ridge caps are separate products, not covered by field-shingle waste.
Does the tool handle multiple roof planes?
Enter the combined horizontal footprint of all planes that share the same pitch. Mixed pitches? Run the tool once per pitch and add the bundle counts — that mirrors how estimators sheet out real roofs.
Roof figures are computed locally and never transmitted. Bundle-per-square sources and the shared pipeline are documented on the methodology page.