Roofing Calculator: Squares, Bundles & Cost

Pitch	Multiplier	Roof area (sq ft)	Squares with waste	Bundles
3/12	1.031	1,385	15.24	46
4/12	1.054	1,417	15.58	47
5/12	1.083	1,456	16.02	49
6/12	1.118	1,503	16.53	50
7/12	1.158	1,556	17.12	52
8/12	1.202	1,615	17.77	54
9/12	1.250	1,680	18.48	56
10/12	1.302	1,749	19.24	58
12/12	1.414	1,901	20.91	63

How to use this calculator

You can measure from the ground or from the roof.

House footprint (the easiest way, done from the ground):

Enter the house’s length (along the ridge) and width, wall to wall.
Enter the pitch as inches of rise per 12 inches of run, for example 6 for a 6/12 roof. If you don’t know it, the roof pitch calculator explains how to measure it.
Enter the overhang, the distance the roof sticks out past the walls.
Choose gable or hip.

Roof planes (if you can measure on the roof or from plans): enter each plane’s length along the eave, its length along the top (the same for a rectangle, 0 for a triangle), and its slope length from eave to ridge.

Then check the waste allowance and, under Materials, the bundles per square, ridge cap coverage and underlayment type printed on the products you plan to use.

The formula

From a footprint, the roof area is the plan area, overhangs included, times the pitch multiplier:

roof area = footprint \times \sqrt{1 + {(\frac{pitch}{12})}^{2}}

Squares are the roof area plus waste, divided by 100. Bundles are squares times bundles per square, rounded up.

The multiplier works for gable and hip roofs alike: when every plane has the same pitch, the surface is always the footprint times the same factor. What the style changes is the edges. On a gable roof the ridge runs the full length, and the sloped rakes at each gable end need drip edge. On a hip roof the ridge is shorter (length minus width), and four hips run down to the corners, each about half the width × √(2 + (pitch ÷ 12)²) long. Those hips need ridge cap shingles too, and they mean more cut shingles, which is why the hip setting starts with 15% waste instead of 10%.

Worked example

The default house is 40 × 30 feet, with a 6/12 gable roof and 12 inch overhangs:

With overhangs: 40 + 2 = 42 ft by 30 + 2 = 32 ft.
Footprint: 42 × 32 = 1,344 sq ft.
Pitch multiplier at 6/12: √(1 + 0.5²) = 1.118.
Roof area: 1,344 × 1.118 = 1,502.64 sq ft.
With 10% waste: 1,652.9 sq ft = 16.53 squares.
Shingles: 16.53 × 3 = 49.59, so 50 bundles.
Synthetic underlayment, 10 squares a roll: 2 rolls.
Ridge cap: 42 feet of ridge at 25 feet per bundle: 2 bundles.

At the example price of $500 per square installed, that’s about $8,265. As a hip roof with 15% waste, the same house needs 17.28 squares, 52 bundles and 5 bundles of ridge cap for its 106 feet of ridge and hips.

The same house at other pitches

Footprint 42 × 32 ft with overhangs, 10% waste, 3 bundles per square:

Pitch	Multiplier	Roof area	Squares	Bundles
3/12	1.031	1,385 sq ft	15.24	46
4/12	1.054	1,417 sq ft	15.58	47
5/12	1.083	1,456 sq ft	16.02	49
6/12	1.118	1,503 sq ft	16.53	50
8/12	1.202	1,615 sq ft	17.77	54
10/12	1.302	1,749 sq ft	19.24	58
12/12	1.414	1,901 sq ft	20.91	63

A steep 12/12 roof has 41% more surface than its footprint. Steep roofs also take longer to work on safely, so the price per square usually rises with the pitch.

Material data used

Bundles per square: 3. Owens Corning says architectural shingles are generally packaged three bundles per square, and its TruDefinition Duration line lists 3 bundles covering 98.4 square feet. GAF lists 3 bundles per square for Timberline HDZ. Some heavier designer shingles come four or five bundles to the square, so check the wrapper and change the setting if needed.
Ridge cap: 25 linear feet per bundle. GAF Seal-A-Ridge bundles are sold as covering 25 linear feet; Owens Corning ProEdge as 33. Enter the figure on the bundle you buy.
Underlayment: Owens Corning notes that synthetic underlayment comes in 10-square rolls and #15 felt in 4-square rolls.
Low slopes: under the International Residential Code, asphalt shingles need a slope of at least 2/12, and slopes from 2/12 up to 4/12 need two layers of underlayment. The calculator doubles the underlayment in that range and warns below 2/12.

Tips before you call a roofer

Measure the footprint from outside, around the walls, and look at the eaves to estimate the overhang.
Count the extras. Starter strip, drip edge, ice and water shield in cold climates, flashing, vents and nails are separate line items. The calculator lists drip edge from the eave and rake lengths.
Compare quotes per square. Ask each contractor how many squares they measured; differences often come from waste allowances and the number of layers to tear off.
Financing a replacement? Our home equity loan calculator and HELOC calculator show what borrowing would cost.

Assumptions and limitations

Footprint mode assumes a simple rectangular house with one pitch on every plane and the same overhang all around. For L-shaped houses, dormers or mixed pitches, measure the planes or add the sections separately.
Gable ridges are assumed to run along the length you enter.
Valleys, chimneys and skylights aren’t modeled; raise the waste allowance for cut-up roofs.
The installed price per square is an editable example, not a market claim. A roofer’s measurement is the one to order from.

Sources

This is a planning estimate, not a roofing bid. Have a licensed contractor measure and inspect the roof before you order or sign.

Frequently asked questions

What is a roofing square?

A square is 100 square feet of roof surface. Roofers price and order shingles by the square, so a 1,500 square foot roof is 15 squares before waste. Architectural shingles typically come three bundles to the square.

How many bundles of shingles do I need?

Divide the roof area by 100 to get squares, add a waste allowance, and multiply by the bundles per square printed on the shingle wrapper, usually 3. A 1,503 square foot roof with 10% waste is 16.53 squares, which is 49.6 bundles, so you'd buy 50.

How do I calculate roof area from the house footprint?

Add the overhang to the length and width, multiply them to get the footprint, then multiply by the pitch multiplier, √(1 + (pitch ÷ 12)²). At 6/12 the multiplier is 1.118, so a 42 by 32 foot footprint has about 1,503 square feet of roof.

Does a hip roof need more shingles than a gable roof?

For the same footprint and pitch, a hip roof has the same surface area as a gable roof, because every plane is tilted by the same angle. It does need more cutting along the hips, so the waste allowance is usually higher, about 15% instead of 10%, and it needs more ridge cap.

How much waste should I add for shingles?

Owens Corning suggests adding 10% to 15% to your material totals. Use about 10% for a simple gable roof and 15% or more for hip roofs or roofs with valleys, dormers and skylights.

How much does a new roof cost per square?

It varies widely by region, shingle line, roof steepness, how many layers are torn off and how complex the roof is. The calculator uses $500 per square installed purely as an editable example; replace it with quotes from local contractors to compare like with like.

Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.

Roofing materials

This footprint at other pitches