Roofing Calculator

Estimate your roof area and the shingles, underlayment, ridge cap and drip edge you need, from the footprint and the pitch.

Feet + inches
Sourced data
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Calculator

Footprint length

Include the overhangs

Footprint width

Include the overhangs

Roof type

Pitch (rise per 12 in of run)

Shingle type

Price per bundle (optional)

Shingle bundles

14.8 squares including 10% waste

Roof surface area: 1,342 sq ft
Pitch factor (6/12): × 1.118
Roofing nails (4 per shingle): ~4,723

Synthetic underlayment

2 rolls

10 sq rolls · or 4 rolls of #15 felt

Ridge cap

40 ft

linear feet

Drip edge

147 ft

15 pieces of 10 ft

Starter strip

80 ft

along the eaves

How it works Formula, reference tables and pro tips

Roof pitch multipliers

Multiply the flat footprint (with overhangs) by this factor to get the sloped roof area.

Pitch	Angle	Multiplier
2/12	9.5°	1.014
3/12	14.0°	1.031
4/12	18.4°	1.054
5/12	22.6°	1.083
6/12	26.6°	1.118
7/12	30.3°	1.158
8/12	33.7°	1.202
9/12	36.9°	1.250
10/12	39.8°	1.302
12/12	45.0°	1.414

What goes on a shingle roof

Underlayment over the whole deck: synthetic rolls usually cover 10 squares; #15 felt about 4 squares and #30 felt about 2 squares per roll.
Ice and water shield along eaves and valleys in cold climates, where code requires it.
Drip edge on eaves and rakes, sold in 10 ft pieces.
Starter strip along the eaves (and often the rakes).
Ridge cap shingles over ridges and hips, plus ridge vents if your attic is vented that way.

Minimum slope for asphalt shingles

The International Residential Code (R905.2.2) allows asphalt shingles only on slopes of 2/12 or steeper. Between 2/12 and 4/12, a double layer of underlayment is required. Flatter roofs need membrane roofing instead.

Quick answers

What is a roofing square?

A square is 100 square feet of roof surface. Shingles are priced and packaged by the square: most 3-tab and standard architectural shingles come 3 bundles to a square, while heavier designer shingles can take 4 or 5 bundles.

How do I measure my roof without climbing on it?

Measure the footprint of the house from the ground, adding the overhangs on each side, then multiply by the pitch factor for your roof's slope. That gives the true sloped area for both gable and hip roofs with a single pitch.

How do I find my roof pitch?

Pitch is the rise in inches for every 12 inches of horizontal run. From inside the attic, hold a level horizontally against a rafter, measure 12 inches along it, and measure straight up to the underside of the rafter. That number over 12 is your pitch.

How much waste should I add for shingles?

About 10% for simple gable roofs and 12–15% for hip roofs or roofs with valleys and dormers, because of the extra cuts. Suppliers don't sell partial bundles, so always round up.

How many nails per square?

With the standard 4-nail pattern, about 320 nails per square (80 shingles × 4). High-wind areas require 6 nails per shingle, or about 480 per square. Follow the instructions on the shingle wrapper.

Sources

Last reviewed November 2, 2026.

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These calculators give estimates for planning and shopping. Product yields, densities and coverage vary by brand and site conditions, so check the label and your supplier. For structural work, follow your local building code and permit requirements.