Roofing Calculator: Shingle Bundles, Squares and Pitch

How to use the roofing calculator

1. Measure the footprint, including overhangs. Measure the length and width of the roof from the ground (eave to eave and rake to rake), or measure the house and add the overhang on each side.
2. Enter the pitch. Pitch is the rise in inches for every 12 in of horizontal run, written like 6/12. Not sure? Switch to the Roof pitch tab to calculate it from a rise and run measurement.
3. Choose gable or hip. A gable roof has two slopes and triangular ends; a hip roof slopes on all four sides. Hip roofs have more cutting, so the waste default rises to 15%.
4. Check bundles per square on the shingle wrapper — 3 for nearly all 3-tab and most architectural shingles.

No need to get on the roof: the footprint-times-pitch method gives the same area as measuring every plane, as long as all planes share one pitch.

Roof area, squares and bundles: the formula

A “square” is the roofing industry’s unit: 100 sq ft of roof surface. The slope factor converts flat footprint area to sloped area.

Worked example: how many bundles of shingles?

A 40 × 30 ft gable roof (including overhangs) at 6/12 pitch:

• Footprint: 40 × 30 = 1,200 sq ft
• Roof area: 1,200 × 1.118 = 1,342 sq ft = 13.4 squares
• With 10% waste: 14.8 squares × 3 = 44.3 → 45 bundles
• Ridge: 40 ft → 2 bundles of hip & ridge cap at about 25 ft per bundle
• Drip edge: 80 ft of eaves + 67 ft of rakes = 15 pieces of 10 ft
• Underlayment: 2 rolls of 10-square synthetic

The same footprint as a hip roof has the same area but a 15% waste allowance (47 bundles), a 10 ft ridge plus 90 ft of hips (4 bundles of cap) and 140 ft of eaves.

Re-roofing over an existing layer, or replacing damaged decking? Ask your roofer about local rules — many areas allow at most two layers, and tear-off is often required.

Waste factor and buying tips

• 10% waste for simple gable roofs; 15% for hip roofs; more for many valleys, dormers or skylights.
• Starter strip runs along the eaves (and usually the rakes). Count the linear feet the calculator shows for eaves and rakes and check the coverage on the starter bundle.
• Ridge cap is a separate product for most architectural shingles. Coverage varies by product — for example about 25 linear ft per bundle for GAF Seal-A-Ridge and 33 ft for Owens Corning ProEdge — so enter the figure from the wrapper.
• Low slopes need extra protection. Asphalt shingles generally require a pitch of at least 2/12; between 2/12 and 4/12, manufacturers and the IRC call for double-layer underlayment.
• Ice barrier is required along the eaves in many cold-climate areas; it’s sold by the roll and isn’t included here.
• Order a few extra bundles from the same lot for future repairs — shingle colors change over time.

Building a deck or porch at the same time? See the deck calculator.

How to measure roof pitch

From the attic or at a gable end, hold a 12 in level horizontally against the underside of a rafter (or on the roof surface from a ladder). Measure straight up from the 12 in mark to the rafter — that number is the rise, and the pitch is rise/12. If you can only measure a different run, the calculator’s Roof pitch tab scales it: a 3 in rise over a 6 in run is 6/12. For degrees, percent slope, rafter length and a full pitch chart, use the dedicated roof pitch calculator.

Above about 8/12, roofs are hard to walk safely and roofers use roof jacks and fall protection. Measure from the ground or the attic whenever you can.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• Sloped roof area = plan area × slope factor, where slope factor = √(1 + (rise ÷ 12)²).
• One square = 100 sq ft. Most 3-tab and architectural shingles come 3 bundles per square; heavier lines can be 4 or 5, so check the wrapper and pick 3, 4 or 5 in the tool.
• Ridge cap defaults to 25 linear ft per bundle (GAF Seal-A-Ridge: 4 bundles cover 100 linear ft); other brands differ, so you can change it.
• Default waste is 10% (use more for hips and valleys). Squares and bundles are rounded up.

Sources

1. GAF, How Many Bundles of Shingles Are in a Square?. A square is 100 sq ft; most asphalt shingles are 3 bundles per square; add 10–15% for waste.
2. IKO, Cambridge Cool Colors Plus contractor brochure. Example spec: 100 sq ft per 3 bundles (33⅓ sq ft per bundle).
3. GAF, Seal-A-Ridge Ridge Cap Shingles sell sheet. 4 bundles cover 100 linear feet of hip and ridge.
4. International Code Council, 2021 International Residential Code, Chapter 9 (Section R905.2, Asphalt Shingles). Code requirements for asphalt shingle roofs (slope, underlayment, fastening).

Last reviewed October 25, 2026. Product figures vary by brand; the label on what you buy wins.