What is Roofing Calculator?

Estimate roofing materials for your project by entering roof dimensions, shape, and pitch. Calculates bundles, squares, underlayment rolls, ridge caps, nails, and drip edge linear footage — and optionally a total material cost when you enter a price per square.

Pick a roof shape (gable, hip, or shed) so the ridge cap and hip rafter footage match the actual geometry. A hip roof needs ridge cap along the long ridge plus four diagonal hip rafters; a shed has none. Pitch runs from 1/12 (almost flat) all the way to a steep 24/12, with the angle in degrees shown beside each ratio, and converts horizontal footprint into actual slope area since a steep roof has noticeably more surface than its footprint. Material switches between 3-tab, architectural, metal panels, clay tile, wood shakes, and slate, so bundle, piece, and nail counts match what the supplier sells. Set the roof complexity (simple, moderate, or complex) to load a sensible waste factor, then fine-tune the slider. Drop in a price per square in your local currency and the tool multiplies it by ordered squares to give you a budgeting figure to take to the supply yard. Turn on attic ventilation and it sizes the net free vent area you need under the 1/300 code rule, split half to the soffit intake and half to the ridge exhaust.

How to use

1. Enter your roof length, width, and select the roof pitch (rise over run).
2. Choose the roofing material type and set the waste percentage (10–15% typical).
3. Review the materials list with quantities and download or print the estimate.

When to use

• Pricing out a re-roof and need a parts list to take to the supply yard.
• Sanity-checking a contractor's bid before signing — squares should roughly match.
• Estimating a shed, garage, or addition where it's not worth hiring a takeoff.

Result

A 40×30 ft ranch house with 6/12 pitch: roof area = 1,342 sq ft (with pitch factor). Needs 14 squares, 42 bundles of 3-tab shingles, 5 rolls of underlayment, and ~28 lbs of nails.

FAQ

Why does pitch change the material count so much?

A 6/12 pitch adds about 12% to the footprint area, and a 12/12 pitch adds 41%. The calculator multiplies your footprint by the slope factor, so a steeper roof needs proportionally more shingles, underlayment, and nails than a low-slope one.

What does a roofing square actually mean?

A square equals 100 square feet of finished roof surface. Shingle bundles are sold so that three bundles cover one square for 3-tab and four for architectural. Suppliers quote prices per square, so it's the unit you want when getting bids.

How much waste should I add?

10% is standard for a simple gable roof. Bump it to 15% for hips, valleys, or a roof with lots of dormers and penetrations — there are more cuts, more starter pieces, and more half-used bundles. Steep complex roofs sometimes need 20%.

Does this include flashing, drip edge, or vents?

Drip edge linear footage is listed — it equals the full roof perimeter, which covers eaves and rakes for shingle jobs. Ridge cap quantity reflects the actual ridge plus any hip rafter length when you pick a hip roof. Turn on the attic ventilation section and it sizes the net free vent area required by the 1/300 building-code rule, split evenly between soffit intake and ridge exhaust. Step flashing, valley flashing, pipe boots, and gable trim still depend on details the calculator does not ask about, so count those from your roof plan separately.

Are the nail estimates per square or total?

Total pounds for the whole roof, assuming four nails per shingle (six in high-wind zones). Roughly 2.5 lbs of 1¼″ roofing nails cover one square for standard installation. Buy a bit extra — nails are cheap and you don't want to run out mid-row.

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