How do I calculate the area of my roof?

Multiply the length and width of the house, including the overhang, to get the footprint, then multiply by the pitch factor. For a 6:12 pitch the factor is 1.118. A 40 by 30 foot house with a 1 foot overhang has a footprint of 1,344 square feet and a roof of about 1,503 square feet.

What is a roofing square?

A roofing square is 100 square feet of roof. Contractors quote shingles and labor per square, so a 1,503 square foot roof is about 15 squares.

How many bundles of shingles are in a square?

Most architectural and three-tab shingles come three bundles to a square, so a roof of 16.5 squares with waste needs about 50 bundles. Some heavier or premium shingles need four bundles to a square, so read the package.

How do I find my roof pitch?

Place a level 12 inches long against the roof, level it and measure the vertical distance from the end of the level to the roof. That distance is the rise in a pitch such as 6:12. You can also find it in the house plans or from a measurement report.

How much extra should I order?

Order about 10% extra for a simple gable roof, 15% for a hip roof and 20% for a roof with many valleys, dormers or chimneys. The extra covers cuts, the starter course, the ridge cap and mistakes.

How low can the pitch be for asphalt shingles?

Under the International Residential Code, asphalt shingles are used on slopes of 2:12 or more, and roofs from 2:12 to less than 4:12 need double underlayment or another approved method. Your local building department has the final word.

Does this include ridge caps, drip edge and flashing?

It adds an extra percentage that covers the starter course and ridge cap, but it does not count drip edge, flashing, vents or nails. Ask your supplier for those, based on the perimeter and the details of your roof.

🏠 Home & Garden

Roofing Calculator · Roof Area, Squares and Shingle Bundles

A roof is measured in squares, where one square is 100 square feet, and shingles are sold in bundles, usually three to a square. The hard part is the area: a pitched roof is larger than the house under it, and the steeper it is, the larger it gets. This calculator turns the size of your house, the overhang and the pitch into roof area, roofing squares, bundles of shingles and rolls of underlayment.

Enter the length and width of the house in feet, the overhang in inches and the pitch, which is how many inches the roof rises for every 12 inches it runs. A 6:12 pitch is common. The calculator finds the footprint with the overhang and multiplies it by the pitch factor, 1.118 for 6:12. Add an extra for cuts, the starter course and the ridge: about 10% for a simple gable, 15% for a hip roof and 20% for a roof with many valleys or dormers. If you already know the roof area, for example from a measurement report, switch to square feet.

The method is exact for a gable or a hip roof with the same pitch on all sides, and an approximation for roofs with dormers or several levels. Treat the result as a planning number, confirm it with your roofer or supplier, and check your local code, which sets the minimum pitch and the underlayment required for shingles. Prices are examples that you should replace with a quote.

What Do You Know?

House Length (feet)

The outside length of the building under the roof

House Width (feet)

Standard: 30

Roof Overhang (inches)

How far the roof extends past the wall; 12 to 24 inches is common

Roof Pitch (rise per 12 inches of run)

Extra for Cuts, Starter and Ridge (%)

About 10% for a simple gable, 15% for a hip roof, 20% for a roof with many valleys or dormers

Underlayment Roll Coverage (square feet)

Printed on the roll. Many synthetic rolls cover 1,000 sq ft

Price per Bundle of Shingles ($)

Example price only. Check your supplier

House size:

Pitch:

Roof shape:

Detailed Breakdown

8 metrics

PRIMARY RESULT

50 bundles

Shingle Bundles to Buy

Roof Area

1,503 square feet

Roofing Squares

15.03 squares

Squares With 10% Extra

16.53 squares

Pitch

6:12 (26.6°, factor 1.118)

Footprint With Overhang

1,344 square feet

Underlayment Rolls (One Layer)

2 rolls

Shingle Cost (50 × $35.00)

$1,750.00

Behind this is dedication and a desire to help

ClaruSite is 100% free and independent. Your support helps keep these financial tools fast, accurate, and available to everyone.

Donate with PayPal

exploreReal-World Scenarios

When to Use This Calculator

Everyday financial situations where this tool gives you fast, accurate clarity:

🏠

Estimate a Reroof

Get the squares and bundles of shingles from the size of the house and the pitch.

📐

See How Pitch Changes the Area

Compare 4:12, 6:12, 8:12 and 12:12 for the same house.

📋

Check a Contractor Quote

Compare the squares in a quote with your own estimate.

💵

Budget the Materials

Add a price per bundle and see the shingle cost and the underlayment rolls.

Calculation Formula

Standard Method

Footprint = (Length + 2 × Overhang) × (Width + 2 × Overhang), with the overhang in feet Pitch factor = √(1 + (Rise ÷ 12)²), for a rise of 6 in 12 the factor is 1.118 Roof area = Footprint × Pitch factor Roofing squares = Roof area ÷ 100 With extra = Squares × (1 + Extra %) Bundles of shingles = Squares with extra × 3, rounded up Underlayment rolls = Roof area ÷ Roll coverage, rounded up (one layer) Cost = Bundles × Price per bundle Three bundles per square is typical for architectural and three-tab shingles, and some premium products need four, so check the package. The pitch angle is arctan(Rise ÷ 12).

Benchmark Example:

A 40 ft by 30 ft house with a 12 inch overhang, a 6:12 pitch and 10% extra: • Footprint with overhang: 42 × 32 = 1,344 square feet • Pitch factor for 6:12: 1.118 • Roof area: 1,344 × 1.118 = 1,503 square feet, or 15.03 squares • With 10% extra: 16.53 squares • Bundles of shingles: 16.53 × 3 = 49.6, so 50 bundles • Underlayment: 1,503 ÷ 1,000 = 1.5, so 2 rolls • Cost at $35 a bundle: 50 × $35 = $1,750 for the shingles The same house with a 12:12 pitch and 15% extra for a hip roof has 1,901 square feet of roof, 21.86 squares and needs 66 bundles. A steeper pitch adds area, which is why the pitch matters more than the size of the house alone.

Frequently Asked Questions

7 answers

Applicable Laws & Regulatory Standards

International Code Council & ASTM International

Official Legal Reference

International Residential Code (IRC) §R905.2 — Asphalt shingles

Allows asphalt shingles on roofs of 2:12 pitch or more and requires double underlayment on slopes from 2:12 to under 4:12, which is why this calculator warns about low-slope roofs.

ASTM D3462/D3462M — Standard Specification for Asphalt Shingles Made From Glass Felt and Surfaced With Mineral Granules

Defines the glass-felt asphalt shingles sold in the United States, the product that the three-bundles-per-square estimate in this calculator is based on.

ASTM D226/D226M — Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing

Covers the felt underlayment installed under shingles, whose roll coverage is the basis for the underlayment estimate.

Legal citations and statutes are provided for consumer transparency, analytical validation, and educational reference under U.S. consumer financial regulations. This tool is not a substitute for formal legal, accounting, or tax counsel.

💡

Found an error or have a suggestion?

Help us calibrate this tool for US regulations and consumer standards.

Send Feedback

Related Calculators for Better Decisions

Mulch, Gravel & Topsoil Calculator · Cubic Yards, Bags and Tons Paint Calculator · How Many Gallons Do You Need?Tile & Flooring Calculator · How Many Tiles and Boxes Do You Need?Square Footage Calculator · Rooms, Walls and Irregular Lots