Answer: Enter your values and the Roofing Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Shingle squares, underlayment rolls, ridge caps & nails
This roofing calculator converts your roof's dimensions and pitch into squares — the trade's unit of measurement — then estimates bundles of shingles, rolls of underlayment, ridge cap, and nails. All math runs locally in your browser.
Roofing material is never quoted in square feet by professionals; it is quoted in squares, and once you speak that language, comparing bids and ordering materials becomes straightforward.
One roofing square covers 100 square feet. Sloped roof area = footprint area × pitch multiplier (for example, sqrt(144+36) ÷ 12 = 1.118 at a 6/12 pitch). Squares = sloped area ÷ 100. Shingles come three bundles to the square for standard three-tab products, so bundles = squares × 3, then add 10 percent for waste at valleys, hips, and rakes.
Underlayment comes in rolls that commonly cover 400 square feet (four squares) with the required overlap, so rolls = squares ÷ 4 rounded up. Ridge and hips take special cap shingles — figure roughly one bundle of hip/ridge cap per 35 to 40 linear feet. Nails go at about 320 per square for standard four-nail application, which is close to one standard 5-pound coil or 1-pound stick box per square; caps, starter course, and drip edge sit on top of that.
This table shows computed material counts at common roof sizes, using three bundles per square, a 10 percent waste allowance, and four-square underlayment rolls. A 20-square roof, for instance, needs 60 bundles before waste and 66 after — buy the 66.
Your own numbers come from the same formulas: squares × 3 × 1.1 for bundles, squares ÷ 4 rounded up for underlayment, and squares × 320 for nails.
| Squares | Sloped area (sq ft) | Bundles @ 3/sq | Bundles +10% waste | Underlayment rolls @ 4 sq |
|---|---|---|---|---|
| 10 | 1,000 | 30 | 33 | 3 |
| 20 | 2,000 | 60 | 66 | 5 |
| 25 | 2,500 | 75 | 82 | 7 |
| 30 | 3,000 | 90 | 99 | 8 |
Measure each roof plane's length and width from the ground or a ladder, multiply per plane, and add them. For complex roofs with hips and valleys, measure every plane separately — a dormer adds two or three small planes plus valley waste on each.
Do not subtract skylights and chimneys from shingle quantities; the flashing and cuts around them consume nearly as much material as the hole removes. If your existing shingles have three or more layers, removal and dumpster costs may rival the material budget — most codes allow no more than two overlay layers before a tear-off is required.
A realistic material list includes starter strip (or shingles reversed as starter) along eaves, ice-and-water shield at eaves and valleys in cold climates, drip edge on all edges, pipe boots and step flashing, ridge vent if you are venting, and sealant. These ancillary items commonly total 15 to 25 percent of the shingle cost.
Labor typically runs more than materials on a full tear-off and replace: published industry cost surveys consistently place total professional replacement for an average home in the low-to-mid five figures in the US, varying with region, pitch, and layers removed. Always get itemized bids that list squares, tear-off layers, and flashing work separately so quotes are comparable.
['A replacement is the moment to fix ventilation. Balanced attic ventilation means net free area split roughly half intake at the soffits and half exhaust at the ridge: a common guideline is 1 square foot of net free vent area per 150 square feet of attic floor (adjustable to 1/300 with a proper vapor retarder and balanced layout). Ridge vents come rated in net free area per linear foot, which turns that guideline into a purchase count.', 'Layer your budget in the order water hits the roof: underlayment (and ice-and-water shield at eaves and valleys in snow regions), then starter and field shingles, then hip/ridge cap, then flashing details at walls and penetrations, then ventilation. Homeowners comparing bids should ask which layers each quote includes — a cheap bid often omits ice shield, new flashing, or ventilation that the next bid properly includes.', 'Scheduling matters too. Roofing needs dry weather and moderate temperatures: most asphalt shingle manufacturers specify installation between roughly 40 and 90 degrees Fahrenheit, since cold shingles crack when nailed and hot ones scuff. Book contractors in late spring or early fall for the best combination of availability and working conditions.']
How many bundles of shingles make a square?
Standard three-tab shingles come three bundles per square (100 sq ft). Heavier architectural products may also be three bundles per square in most lines, but always check the bundle coverage printed on the wrapper — a few premium lines require four or more.
How do I calculate how many squares my roof is?
Multiply each plane's length × width in feet, sum all planes, then divide by 100. If you only know the footprint, multiply by the pitch multiplier first — for example, a 1,200 sq ft footprint at 6/12 pitch is 1,200 × 1.118 = 1,342 sq ft ≈ 13.4 squares.
How much waste factor should I add for shingles?
Ten percent is standard for gable roofs; use 12 to 15 percent for roofs with multiple hips, valleys, and dormers, since every intersecting edge produces cutting waste. Round bundles up to full units — leftovers are returnable at most suppliers.
How many nails do I need per square of shingles?
Standard four-nail application for three-tab shingles uses about 320 nails per square (four nails per shingle, with three tabs per strip and 26 strips per bundle). High-wind areas specify six nails per shingle, which raises the count roughly 50 percent.
What is a square in roofing?
A square is 100 square feet of roof area — the universal quoting unit in US roofing. A 2,000 square foot roof is 20 squares, and shingle bundles, underlayment rolls, and labor rates are all priced against it.