Calculators · Roofing Calculator

Roofing

Roofing Calculator

Enter the footprint and pitch of your roof to get its area in square feet, roofing squares and the number of shingle bundles.

Section 1

Footprint length

Footprint width

Roof pitch

Overhang (optional)

Added on every side of every section. With several sections the overhang is added to every side of each one, including where they meet. For an L-shaped house, add the overhang to the outer measurements and leave this box empty.

Waste to add (%)

Optional. Empty means 0. See the waste guide below.

Shingle bundles per roofing square

Check the package of your shingles. The figures come from GAF and Owens Corning.

How to calculate roof area from the footprint

A sloped roof is bigger than the floor plan under it. Measure the footprint, which is the length and width of the part of the house the roof covers, then multiply by the pitch factor:

Step	Formula
Pitch factor	√(1 + (rise ÷ 12)²)
Roof area	footprint area × pitch factor
Roofing squares	roof area ÷ 100
Pitch in degrees	arctangent of (rise ÷ 12)

The result is the same for a gable roof and a hip roof as long as every plane has the same pitch. If an addition or a dormer has a different pitch, add it as its own section with its own pitch. For an overhang, add it to each side of the footprint before applying the factor. The calculator does that for you.

Roof pitch factors and angles

Pitch	Pitch factor	Angle
4/12	1.0541	18.4°
5/12	1.0833	22.6°
6/12	1.1180	26.6°
7/12	1.1577	30.3°
8/12	1.2019	33.7°
9/12	1.2500	36.9°
10/12	1.3017	39.8°
11/12	1.3566	42.5°
12/12	1.4142	45.0°

Example: a 30 ft by 40 ft house with a 6/12 roof

A house has a footprint of 30 ft by 40 ft, no overhang, and a 6/12 roof pitch. You will use shingles that come 3 bundles per square and want to add 10% waste.

Step	Operation	Result
Footprint	30 × 40	1,200 sq ft
Pitch factor	√(1 + (6 ÷ 12)²)	1.1180
Roof area	1,200 × 1.1180	1,341.64 sq ft
Roofing squares	1,341.64 ÷ 100	13.42
With 10% waste	13.42 × 1.10	14.76 squares
Bundles	14.758 × 3 = 44.27, rounded up	45 bundles

Roof area by footprint and pitch

Footprint	4/12	6/12	8/12	12/12
1,000 sq ft	1,054 (10.5 sq)	1,118 (11.2 sq)	1,202 (12.0 sq)	1,414 (14.1 sq)
1,500 sq ft	1,581 (15.8 sq)	1,677 (16.8 sq)	1,803 (18.0 sq)	2,121 (21.2 sq)
2,000 sq ft	2,108 (21.1 sq)	2,236 (22.4 sq)	2,404 (24.0 sq)	2,828 (28.3 sq)
2,500 sq ft	2,635 (26.4 sq)	2,795 (28.0 sq)	3,005 (30.0 sq)	3,536 (35.4 sq)

Roof area in square feet, with roofing squares in brackets. No overhang and no waste.

Roofing squares and shingle bundles

Roofers measure and price shingles by the roofing square, which is 100 square feet of roof. Shingles are heavy, so manufacturers package them in bundles that are easier to lift. The number of bundles in a square depends on the product. These are the figures we checked in October 2026:

Product	Bundles per square	Source
GAF Timberline HDZ	3	GAF
Owens Corning TruDefinition Duration	3	Owens Corning
GAF Woodland	4	GAF
Heavy specialty shingles	up to 5	GAF

Owens Corning lists a coverage of 98.4 square feet per square for Duration, so the exact figure for a product can differ a little from 100. Read the coverage printed on the bundle you buy. This calculator rounds the bundle count up, because you cannot buy part of a bundle.

How much waste to add

Leave the waste box empty to see the exact area. The published advice varies:

GAF suggests adding 10-15% to the material total for trim allowance and waste, and adds that a steep slope, rakes, valleys and dormers call for more material than the area alone suggests.
Fine Homebuilding author Mike Guertin figures about 1% on a simple roof and 5% or more on a complex roof with open valleys. He works out starter shingles and hip and ridge caps separately, and adds extra shingles for valleys.

The same article says one bundle of 3-tab shingles caps about 35 linear feet of ridge or hip. Those caps are not part of this calculation, so add them to your order on top of the bundles shown above. Figures checked in October 2026.

What this calculator does not do

It estimates area, squares and shingle bundles from the measurements you type. It does not give prices, and it does not count hip and ridge caps, starter strips, underlayment, flashing or drip edge. For those, use the roof area and the squares above and ask your supplier for the coverage of each product.

Frequently asked questions

How do I calculate roof area from the footprint?

Multiply the footprint (length × width) by the pitch factor, which is the square root of 1 plus (rise ÷ 12) squared. A 30 ft by 40 ft footprint is 1,200 square feet. At a 6/12 pitch the factor is 1.118, so the roof area is 1,200 × 1.118 = 1,341.64 square feet, or 13.42 roofing squares.

How many square feet are in a roofing square?

One roofing square is 100 square feet of roof area, a 10 ft by 10 ft patch. A roof of 1,341.64 square feet is 13.42 squares.

How many bundles of shingles are in a square?

Most standard asphalt shingles, both 3-tab and architectural, come three bundles to a square. GAF says its Woodland line comes four bundles to a square and that some specialty shingles may need up to five because of their weight. Read the coverage printed on your package, since it is the number that counts for your product.

How much waste should I add when I order shingles?

The sources disagree, so ask your supplier or the shingle manufacturer. GAF says to add 10-15% for trim allowance and waste. Fine Homebuilding author Mike Guertin figures about 1% on a simple roof and adds 5% or more on a complex roof with open valleys, while ordering starter and ridge shingles separately. Type the figure you choose in the waste box.

How do I measure roof pitch?

Pitch is the rise in inches for every 12 inches of horizontal run, written as 6/12, for example. If you know the angle instead, choose degrees in the pitch menu and the calculator converts it. Check the plans of the house if you have them, or measure on the roof itself with a level and a tape.

Can I get my roof measurements from Google Maps or a satellite?

Not with this calculator. It does not read addresses or satellite images. You type the footprint and the pitch, and the math runs in your browser, so nothing you enter is sent anywhere.

Does this work for a metal roof?

The roof area and the number of squares come from geometry, so they are valid for any roofing material. The bundle count only applies to asphalt shingles. For metal, use the roof area and follow the coverage given by the panel manufacturer.