Turn your roof's footprint and pitch into a complete shingle order — squares, bundles, underlayment rolls, ridge caps, drip edge, starter strip and nails, with the pitch multiplier and waste allowance built in.
What Your Results Mean
Everything starts with the footprint: the outline of the building as seen from directly above, measured exterior wall to exterior wall including the eaves' overhang, because the roof extends past the walls. Walk the perimeter with a tape, or pace it — a calibrated pace is accurate to about 3 percent, which is fine for this job. Attached garages and porches count if they're under roof; on a two-storey house, use the largest roofed outline, not the sum of the floors.
Pitch is stated as rise over 12: a "6/12" roof climbs 6 inches for every 12 inches of horizontal run. You don't need a ladder to read it — in the attic, hold a level against a rafter, mark 12 inches along it, and measure the vertical drop at the mark. That drop is your pitch's first number. The multiplier converts your flat footprint into actual sloped surface; it's the hypotenuse of the rise/run triangle, not a fudge factor. Below 6/12 pitch barely matters; above 8/12 it matters a great deal.
Shape decides two things: where the cap line runs, and how much waste the cuts generate. A gable roof has two flat faces, a ridge running the length of the house, and raked edges at the gable ends — cap material follows the ridge only. A hip roof slopes on all four sides, replacing the gable ends with angled hip lines; every one of those lines needs capping, and every one of them generates angled cuts, which is why hip waste defaults to 15 percent against the gable's 12.
Reading the Order
- Squares: The headline number. One square is 100 square feet (9.29 m²) of roof surface; suppliers bundle and sell around it. The calculator shows the exact figure (waste included) and the rounded-up count to order.
- Shingle Bundles: Squares × bundles per square, rounded up — three bundles per square covers most three-tab and architectural lines; heavier architectural products can run four or five. The bundle label states its coverage; when in doubt, order by squares and let the supplier do this multiplication.
- Underlayment Rolls: Squares divided by the coverage printed on the roll. Classic #15 asphalt felt covers about four squares per roll, #30 about two, and synthetics range from five to ten or more — the wrapper states it, and the input accepts whatever it says.
- Cap Bundles: The ridge and hip line, divided by roughly 33 feet of coverage per bundle when caps are cut from three-tab shingles at a 5-inch exposure. Specialty ridge-cap products often cover less — check the stated coverage before cutting the order.
- Drip Edge & Starter: Linear feet along eaves and rakes. Drip edge metal comes in 10-foot pieces (the piece count is shown); starter strip runs the same edges so the first course of shingles has something sealed to seal against.
- Nails: About 320 per square at four nails per shingle, plus the nails that fasten the caps — roughly 5 per linear foot of ridge and hip. High-wind zones require six nails per shingle; add half again if your area is mapped for them.
What the Calculator Does Not Do
This tool counts materials, not money — roofing products and pack sizes vary by region, and quotes are the supplier's job. It models one clean rectangle: for L-shaped or cut-up roofs, run each section separately and add the results, then bump the waste allowance toward 20 percent for the valleys and transitions. It also does not size flashing, ice-and-water membrane at eaves, or specialty vents.
Pro Tip
Order the rounded-up square count, not the decimal. The last square of rounding is sensible insurance — unopened bundles go back to the supplier, while a mid-roof shortage means a second delivery and a crew standing around. The roof measurement guide covers the full method behind every number here.
The Math Behind the Calculator
Roofing quantities are geometry first and shopping second. The chain from your tape measure to the supplier's order form is four multiplications:
footprint = length × width
roof_surface = footprint × pitch multiplier
with_waste = roof_surface × (1 + waste% ÷ 100)
squares = with_waste ÷ 100
bundles = squares × bundles_per_square, rounded up
The pitch multiplier is the hypotenuse of the rise/run triangle — the standard published values used across the roofing industry:
Cap Line Geometry
The ridge and hip lines are where the cut pieces go, and their lengths come straight from the footprint:
- Gable: ridge = building length. Rakes (the sloped gable-end edges) = 2 × (width ÷ 2 × multiplier). Eaves = 2 × length.
- Hip: ridge = length − width (zero on a square hip). Each hip line = (width ÷ 2) × √(2 + (pitch ÷ 12)²). Eaves = 2 × length + 2 × width.
Cap bundles divide that line by about 33 feet — what one bundle of three-tab shingles yields when cut into caps at a 5-inch exposure. Drip edge and starter strip both follow eaves + rakes; drip edge arrives in 10-foot pieces, so the calculator rounds that up too. Nails follow the IRC-style fastening schedule of four nails per shingle (about 320 per square) plus roughly five nails per foot of ridge and hip for the caps.
Assumptions & Limitations
Every number above rests on these constants. If your project differs, change the matching input — or read the linked guide for the full reasoning.
- Pitch multipliers are the standard published industry values (hypotenuse of rise/run)
- Three bundles per square by default — heavier lines run 4–5; the label governs
- Underlayment defaults to #15 felt at four squares per roll — set #30 (2) or synthetic (5–10+) to match your roll
- Ridge caps cut from three-tab at ~33 ft per bundle; specialty cap products cover less
- Nails at 4 per shingle (~320/square) plus 5 per foot of caps — high-wind zones need 6 per shingle
- One rectangle per calculation — for L-shapes and cut-up roofs, run each section and add
Worked Example: 28 × 44 ft Gable at 6/12
A rectangular house, 28 feet wide by 44 feet long, gable roof at a 6/12 pitch — the same roof walked through in the roof measurement guide, so every number below is checkable against it. Enter 44 × 28, pitch 6/12, shape gable, and leave the waste at the 12 percent gable default:
- Footprint: 28 × 44 = 1,232 sq ft.
- Multiplier at 6/12: × 1.118 = 1,377 sq ft of sloped roof.
- Waste at 12%: 1,377 × 1.12 = 1,543 sq ft → 15.4 squares — order 16.
- Bundles: 15.4 × 3 = 46.3, rounded up to 47 bundles.
- Underlayment: 15.4 ÷ 4 = 3.9, rounded up to 4 rolls of #15 felt.
- Cap line: the ridge, 44 ft → 44 ÷ 33 = 2 cap bundles.
- Drip edge and starter: 88 ft of eaves + 31 ft of rakes = 119 ft (12 pieces of 10-ft metal).
- Nails: 15.4 × 320 + 44 × 5 ≈ 5,160.
Now switch the shape to hip — same footprint, 30 × 24 ft on a 6/12, waste at the 15 percent hip default. The footprint of 720 sq ft becomes 805 sq ft of surface, 926 with waste — 9.3 squares, order 10, or 28 bundles. The cap line changes character entirely: a 6-foot ridge plus four 18-foot hip lines, 78 feet in all, needing 3 cap bundles. Eaves run the full perimeter, 108 feet of drip edge and starter, and nails land near 3,350. Same tape measure, same pitch — a different order, which is exactly why the shape input exists.
Notice how the hip's waste-adjusted squares (9.3 on 7.2 squares of footprint) sit 29 percent above the footprint while the gable's sit 25 percent above its own. That gap is the effect of the cuts: hips trade rakes for diagonal seams, and diagonal seams eat shingles. It compounds on cut-up roofs — run the numbers once with 20 percent waste before believing any estimate for a dormered roof.
