Roofing Calculator

How many bundles of shingles you need, in squares, plus underlayment, ice and water shield, drip edge, starter strip, ridge cap and nails.

Inputs

ft
Outside wall to outside wall, measured on the ground.
ft
in
How far the roof sticks out past the walls. 12 in is common.
Inches of rise per 12 in of run. Standard shingles need at least 2/12.
%
About 10% for a simple gable roof; 15% for hip roofs, valleys and dormers.
Check the wrapper: it says how many sq ft one bundle covers.
rows
Each row is 3 ft wide. Cold areas usually need it to reach 24 in inside the wall line (often 2 rows); set 0 where it isn't required.

Results

—bundles of shingles
Roof area—
Squares to buy—
Pitch factor—
Underlayment rolls—
Ice and water shield rolls—
Drip edge—
10 ft drip edge pieces—
Starter strip bundles—
Ridge cap bundles—
Roofing nails—
Assumptions: Roof area = footprint with overhang × pitch factor (√(1 + (rise ÷ 12)²)), which holds when every roof plane has the same pitch. Bundles and squares include the extra % and are rounded up. Underlayment adds 10% for laps. Ice and water shield rolls are 3 × 66.6 ft (200 sq ft) and cover the eaves only; add more for valleys. Starter strip ≈ 120 linear ft per bundle on eaves and rakes; ridge cap ≈ 25 linear ft per bundle; drip edge on eaves and rakes in 10 ft pieces plus 5% for laps. Nails assume 64 shingles per square. Product coverage varies by brand, so check the wrappers. Estimates for planning only; confirm with your supplier.

Roofing calculator FAQ

How many bundles of shingles are in a square?

Most asphalt shingles come 3 bundles to a square, and a square covers 100 sq ft of roof. Some heavy designer shingles take 4 or 5 bundles per square. The wrapper lists how many sq ft one bundle covers.

How many bundles of shingles for a 40 × 30 house?

With a 6/12 gable roof and 12 in overhangs, the roof is about 1,503 sq ft. With 10% extra that's 16.5 squares, or 50 bundles at 3 bundles per square.

How do I figure roof area from the ground?

Measure the house, add the overhang on every side, and multiply length × width. Then multiply by the pitch factor: 1.054 for 4/12, 1.118 for 6/12, 1.202 for 8/12, 1.302 for 10/12 and 1.414 for 12/12.

How much extra shingle should I buy?

About 10% for a simple gable roof and 15% for hip roofs or roofs with valleys and dormers. The extra covers cuts and starter courses at edges.

How many nails per square of shingles?

About 256 nails per square with 4 nails per shingle, or 384 with 6 nails per shingle where high-wind nailing is required.

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Step-by-step guide: How many bundles of shingles do I need? (squares, pitch and roof size chart) — formula, worked examples, and common mistakes.