Roofing squares calculator: shingle bundles and order list
Enter the footprint and pitch, or the roof planes you measured. Get roof squares and a full order list, with the formula and manufacturer figure behind every number.
How it works
Enter the building footprint and pitch, or tape each roof plane. The calculator turns that into sloped roof area and squares, then divides by the coverage printed on each product to build the order list, and "Show your work" repeats the math with your figures. Not sure of the pitch? Measure it with the roof pitch calculator first.
How we calculate it
These are the lines in the "Show your work" panel, in the same order. s is the pitch as a ratio: inches of rise ÷ 12. Lengths are in feet. Each purchase quantity is rounded up once, on its own line. The examples use a 40 × 30 ft gable at 6:12 with 12 in overhangs and 10 % waste.
- Pitch: s = x ÷ 12 and the slope multiplier m = √(1 + s²). At 6:12, s = 0.5000 and m = 1.1180.
- Plan area: gable (length + 2 × rake overhang) × (width + 2 × eave overhang); hip (length + 2 × overhang) × (width + 2 × overhang). Overhangs are measured level. Example: 42 × 32 = 1,344.0 ft².
- Roof area: plan area × m = 1,344.0 × 1.1180 = 1,502.6 ft². This holds only when every plane has the same pitch. In Measured planes mode, each plane line is rectangle base × height, triangle ½ × base × height, or trapezoid ½ × (eave edge + ridge edge) × height, times the number of identical planes. A plane measured level is also multiplied by its own m. The planes are then added up.
- Squares: roof area ÷ 100 = 15.03. A roofing square is 100 ft² of roof surface (ASTM D1079).
- With waste: roof area × (1 + waste ÷ 100) = 1,652.9 ft², or 16.53 squares. Waste is a rule of thumb: about 10 % for a gable, 15 % for a hip and 20 % for a cut-up roof.
- Edges: gable eave = 2 × length, rake = 2 × width × m, ridge = length. Hip eave = 2 × (length + width) and ridge = length − width. All use the dimensions with overhangs. Measured planes mode uses the edge lengths you enter.
- Hips: 4 × (width ÷ 2) × √(2 + s²). The hip factor √(2 + s²) is 1.4530 at 4:12.
- Shingles: area with waste ÷ coverage per bundle. 3 bundles per square is 33.33 ft² per bundle, so 1,652.9 ÷ 33.33 = 49.587 → 50 bundles.
- Starter: (eave + rake) ÷ linear feet per bundle, or eave only if you untick rakes.
- Ridge cap: (ridge + hips) ÷ linear feet per bundle.
- Underlayment: roof area × layers ÷ net coverage per roll. Two layers from 2:12 up to 4:12, one layer at 4:12 and steeper (2021 IRC R905.1.1).
- Ice barrier (when on): reach = eave overhang + wall thickness + 24 in, measured level (2021 IRC R905.1.2). Up the slope = reach × m. Courses = 1 if one roll width covers it, otherwise 1 + (up the slope − roll width) ÷ (roll width − side lap), rounded up. Rolls = courses × eave length ÷ (roll length − end lap). Underlayment is not reduced under the ice barrier.
- Drip edge: (eave + rake) ÷ (piece length − lap). A 10 ft piece with a 2 in lap covers 9.833 ft. The 2021 IRC (R905.2.8.5) requires drip edge at eaves and rakes, lapped at least 2 in.
- Nails: squares without waste × pieces per square × nails per shingle, because waste pieces are not nailed. 15.03 × 64 × 4 = 3,847. Coil boxes are about one per 20 squares to order (GAF estimating worksheet). Starter and cap nails are extra.
- Difference (quote check): (quote squares − squares to order) ÷ squares to order × 100.
Asphalt shingles need a pitch of at least 2:12 (2021 IRC R905.2.2). Below that, the calculator shows area and edges only. The math uses unrounded values, so the last digit may differ from multiplying the rounded numbers shown.
Sources: square = 100 ft² of roof surface (ASTM D1079). Slope multiplier from geometry (see the roof pitch calculator). Coverage figures are from the selected manufacturer's data sheet, so check your wrapper. Drip edge lap, underlayment layers and ice-barrier reach follow the 2021 IRC, Sections R905.2.8.5, R905.1.1 and R905.1.2.
Related: work out pitch, degrees and rafter length with the roof pitch calculator. Contractors can turn the order list into a priced quote with the estimate and invoice generator.
Questions
How many bundles of shingles are in a square?
Most laminated and 3-tab shingles come 3 bundles to a square, for example GAF Timberline HDZ and GAF Royal Sovereign. Some heavier designer shingles take 4 or 5. Owens Corning prints 32.8 ft² per bundle, so 3 bundles cover 98.4 ft², not a full 100. Go by the number on your wrapper. You can type it into the calculator.
How many bundles do I need for a 20 x 20 ft garage?
Measure the roof, not just the walls. A 20 x 20 ft hip roof at 4:12 with 1 ft overhangs is 22 × 22 × 1.0541 = 510 ft², or 5.10 squares. With 15 % waste for a hip, that is 5.87 squares, or 18 bundles of 3-tab at 3 bundles per square. You also need 1 bundle of starter, 3 bundles of hip and ridge cap and 9 pieces of drip edge.
How much waste should I add?
About 10 % for a simple gable, 15 % for a hip roof and 20 % for a roof with valleys and dormers. These are rules of thumb. Owens Corning says 10-15 %, and GAF's estimating worksheet says add 10 %. Add waste to field shingles only. Starter, ridge cap and drip edge are counted by length.
Do I need starter strip on the rakes, or just the eaves?
The major shingle makers require starter on the rakes as well as the eaves for their enhanced wind warranty. The calculator includes rakes by default. Untick the box if your product's instructions say eaves only.
How do I check the squares on my roofing quote?
Enter your footprint and pitch, then type the squares from the quote into "Check a quote". A gap of more than about 10 % is worth asking about. Sheds, detached garages, extra layers or a cut-up roof can explain it. The slope multiplier is only 1.05 at 4:12 and 1.41 at 12:12, so a roof area several times your footprint is a measuring error.