Estimate a whole roof, section by section.

The full calculator turns real roof geometry into a complete, ordered material list. Add one section per roof plane, set each plane's pitch, add any complex features, and it produces a take-off you can hand to a supplier.

How to use this calculator

Roof sections (shape + dimensions)

Each flat plane of your roof, entered as a rectangle, triangle, or trapezoid using footprint (ground) measurements. A gable is two rectangles; a hip is trapezoids plus triangles. Add a section per plane.

Pitch (rise:12) per section

The slope of that plane, as inches of rise over a 12-inch run. Each plane can have its own pitch — the calculator applies the right multiplier to each.

Roof complexity (waste %)

A waste allowance for cuts, valleys, and offcuts: 10% simple, 15% moderate, 20% complex, 25% very complex.

Shingle type

3-tab (3 bundles/square) or architectural, premium, and impact (4 bundles/square). This sets the bundle math.

Eave, rake, ridge & hip (linear feet)

Edge lengths that drive starter strip, drip edge, and ridge-cap quantities.

Complex features (optional)

Chimney and skylight openings to subtract, plus step, valley, and pipe flashing to add.

How we calculate it

Step 1 — true area per plane. Each plane's footprint area (length×width, or the triangle/trapezoid formula) is multiplied by its pitch multiplier, which is √(12² + rise²) ÷ 12. A pitched plane is always larger than its ground shadow, so this correction matters.

Step 2 — net area and waste. Any chimney or skylight openings you entered are subtracted from the summed true area. The remainder is multiplied by (1 + waste%) to get the area you actually buy for.

Step 3 — squares. That area is divided by 100 to convert to roofing squares, the unit the trade orders in.

Step 4 — materials. Shingle bundles = squares × bundles-per-square (3 or 4), rounded up. Underlayment rolls = area ÷ roll coverage. Starter = (eave+rake) ÷ 120.33 lf/bundle. Drip edge = (eave+rake) ÷ 10 ft/stick. Ridge cap = ridge+hip ÷ 25 lf/bundle. Nails = total shingles × 4 (or 6 for high-wind). Each result rounds up to whole units, because you can't buy a partial bundle.

A worked example

A simple gable: two rectangular planes, each 40 ft × 18 ft, at a 6:12 pitch, moderate complexity (15% waste), architectural shingles, with 80 ft of eave, 60 ft of rake, and 50 ft of ridge.

1. Footprint = 2 × (40 × 18) = 1,440 sq ft.
2. 6:12 multiplier = √(144 + 36) ÷ 12 = 1.118. True area = 1,440 × 1.118 = 1,610 sq ft.
3. With 15% waste: 1,610 × 1.15 = 1,851 sq ft → 18.5 squares.
4. Shingles = ceil(18.5 × 4) = 74 bundles. Underlayment (synthetic, 1,000 sq ft/roll) = ceil(1,851 ÷ 1,000) = 2 rolls.
5. Starter = ceil(140 ÷ 120.33) = 2 bundles. Drip edge = ceil(140 ÷ 10) = 14 sticks. Ridge cap = ceil(50 ÷ 25) = 2 bundles.

The take-off lists 74 shingle bundles, 2 underlayment rolls, 2 starter bundles, 14 drip-edge sticks, 2 ridge-cap bundles, and the nail count — each line showing the formula used.

Frequently asked questions