Everyday
Roofing Shingle Calculator
Figure out how many shingle bundles your roof needs, what the accessories cost, and whether DIY or a contractor pencils out better.
How it works
Behind the numbers
Start by measuring each roof plane on the ground plan: length and width in feet, and the pitch as rise per 12 inches of run. Every plane gets its own row, up to six, because a roof is rarely one rectangle. Each plane's area is its length times width times the pitch multiplier, sqrt(1 + (pitch/12)^2), which turns flat plan area into true sloped surface. The calculator adds all planes together for total square footage, then divides by 100 to get roofing squares, the unit the whole industry prices in.
Bundles come from squares and waste. Standard three-tab shingles pack three bundles per square, and each bundle covers 33.3 sq ft, so the field bundle count is total area times (1 + waste) divided by 33.3, always rounded up since bundles are sold whole. The waste percentage covers cuts around valleys and hips, broken shingles, and starter offcuts; 10% suits a simple gable, 15% or more suits a cut-up roof. If your shingle covers a different area per bundle, set it under coverage per bundle and the math follows your product.
Accessories are estimated by linear feet. Ridge and hip lines convert to cap bundles at roughly 35 feet per bundle, starter course at about 100 feet per bundle, and valley flashing, drip edge, and vent boots are priced per foot or per piece with editable prices. The DIY versus contractor switch decides whether labor is added: contractor mode multiplies squares by your per-square labor rate, then the brand comparison divides each quote by its warranty years to show the cheaper cost per year.
FAQ
Questions, answered
How many bundles of shingles do I need?
Divide the roof area, pitch included, by 100 to get squares, then multiply by 3 bundles per square for standard three-tab shingles and add waste. A 1,789 sq ft roof at 6/12 pitch is 17.9 squares, so with 10% waste you buy 60 bundles. Architectural shingles cover less per bundle, so check the wrapper first.
How does roof pitch change the shingle count?
Pitch stretches the surface: multiply each slope's plan area by sqrt(1 + (pitch/12)^2). At 6/12 the multiplier is 1.118, so a 1,600 sq ft footprint becomes 1,789 sq ft of shingle surface before waste. A 12/12 roof needs about 41% more shingles than the same footprint at a walkable pitch.
What waste percentage should I use?
10% is standard practice for a simple gable roof; shingle makers cite 10-15% as the typical range. For cut-up roofs with valleys, dormers, and hips, 15-20% is safer because angled cuts waste more material. Unopened bundles can usually be returned.
What is a roofing square?
One square is 100 square feet of roof surface. Contractors buy and price shingles in squares: a 1,789 sq ft roof is 17.9 squares. Three-tab shingles come 3 bundles to a square (33.3 sq ft per bundle), so squares times 3 is your bundle count before waste.
How do I measure my roof's pitch?
The field method used by shingle makers: hold a 12-inch level against the roof surface, level it, then measure straight down from the free end to the roof. That distance in inches is your pitch, for example 6 means 6/12. Enter that number in the pitch field for each plane.