Roofing Calculator
Work out roof area from pitch, roofing squares, shingle bundles and underlayment, with material and labor cost. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/roofing-calculator
Material prices are 2026 US national averages, estimates only.
3 bundles per square is standard for asphalt shingles.
Labor usually runs $300 to $500 per square.
Leave 0 to use the building length plus overhang.
One roofing square is 100 sq ft of roof surface. Asphalt shingles need a slope of at least 2/12. This is a planning estimate: valleys, dormers, skylights and chimneys need extra material, and a roofer should verify measurements on site.
Quick answer
A roofing calculator works out the materials for a new roof from the building size and the pitch. Enter the length, width, overhang, roof type and pitch, and it shows the sloped roof area, the roofing squares, shingle bundles, underlayment rolls, ridge cap, drip edge and nails, with the material and labor cost.
About this Roofing Calculator
Work out roof area from pitch, roofing squares, shingle bundles and underlayment, with material and labor cost. It is one of the Home and DIY on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a roofing calculator?
A roofing order starts with one number: the true area of the roof surface, measured on the slope. A roof is not flat, so the floor plan area understates it. The calculator gets there from the plan dimensions you already have: it adds the overhang on every side, multiplies the plan area by the slope factor for the pitch, and converts the result to roofing squares. On a 40 by 30 ft building with a 1 ft overhang and a 6/12 pitch, the footprint is 42 by 32 ft, 1,344 sq ft, the slope factor is 1.118, and the roof area is 1,503 sq ft.
The slope factor is the square root of 1 plus the pitch squared over 12 squared. A 2/12 pitch multiplies the footprint by 1.014, 4/12 by 1.054, 6/12 by 1.118, 8/12 by 1.202, 10/12 by 1.302 and 12/12 by 1.414.
Squares, bundles and the rest of the order
One roofing square is 100 sq ft of roof surface, and it is the unit the whole trade uses. Standard 3-tab and most architectural shingles need 3 bundles per square, since each bundle covers about 33 sq ft. Underlayment usually comes in rolls covering 400 sq ft, or 4 squares. Ridge cap comes in bundles covering about 20 linear feet of ridge. Drip edge comes in 10 ft pieces around the whole roof edge. Nails run about 2 lb per square.
What a roof costs, and what the estimate leaves out
Installed asphalt shingles run about $3.40 to $5.95 per sq ft in 2026 US national averages, so a 1,503 sq ft roof is roughly $5,100 to $8,900. Materials are typically $130 per square for 3-tab shingles and $160 for architectural, $450 for standing seam metal and $600 for concrete tile. Labor is usually $300 to $500 per square. Tear-off of the old roof adds $100 to $200 per square.
Best practices
- Add 10 percent waste on a gable, 15 percent on a hip: every diagonal cut wastes a piece of shingle.
- Measure the pitch properly: use a 12-inch level and a tape, or a pitch gauge app, and check in two places.
Common mistakes to avoid
- Ordering by the floor plan area and running short, because the slope adds 12 percent on a 6/12 roof.
- Forgetting the ridge cap, drip edge and nails, which are small lines that still stop a job.
Who is the roofing calculator for?
Homeowners budgeting a re-roof, DIY builders ordering shingles, and anyone comparing quotes from roofers. Prices are 2026 US national averages and vary by region; get a written quote from a roofer before you commit.
Learn: how to use the Roofing Calculator
- Enter the building length and width in feet, plus the overhang on all sides.
- Pick the roof type: gable, hip or shed, and the pitch as rise per 12 inches of run.
- Pick a waste allowance: 10% for a simple gable, 15% for a hip roof, 20% for a complex roof.
- Choose the shingle material, bundles per square and underlayment roll coverage, then add labor and tear-off.
- Read the roof area, squares, bundles, underlayment rolls, ridge cap, drip edge, nails and the total cost.
Features
- Roof area from footprint times the pitch slope factor
- Roofing squares at 100 sq ft each, rounded up to the half square
- Shingle bundles at 3 per square, adjustable
- Underlayment rolls, ridge cap bundles, drip edge pieces and nails
- Four materials with 2026 US national average prices per square
- Labor and tear-off cost, installed cost per sq ft, and a pitch multiplier table
Worked example
A 40 by 30 ft building with a 1 ft overhang, a gable roof at 6/12 pitch: the footprint with overhang is 42 by 32 ft, 1,344 sq ft. The slope factor is 1.118, so the roof area is 1,503 sq ft. With 10% waste, order 1,653 sq ft, which is 17 squares. That is 51 shingle bundles at 3 per square, 5 underlayment rolls at 400 sq ft each, 3 ridge cap bundles for 42 ft of ridge, 15 drip edge pieces for 148 ft, and about 34 lb of nails. Architectural shingles at $160 a square cost $2,720 and labor at $300 a square costs $5,100, for a total of $7,820, or $5.20 per sq ft.
Frequently asked questions
What is a roofing square?
One roofing square is 100 square feet of roof surface. Shingles, underlayment and labor are all quoted by the square, so a 1,503 sq ft roof is 17 squares after waste. It is the standard quantity roofers use.
How many bundles of shingles per square?
Three bundles per square for standard 3-tab and most architectural shingles, since each bundle covers about 33 sq ft. Always round up to a whole bundle, and check the label: some heavy architectural shingles need 4 bundles per square.
How do I calculate roof pitch?
Pitch is the rise in inches over 12 inches of run. Measure 12 inches along a level from the roof surface, then measure straight up to the roof: 6 inches of rise is a 6/12 pitch. A 6/12 pitch multiplies the footprint by 1.118.
How much waste should I add?
10% for a simple gable roof, 15% for a hip roof or one with many cuts, and 20% for a complex roof with valleys and dormers. Every diagonal cut wastes a piece, so cut-up roofs need more.
How much does a new roof cost?
Installed asphalt shingles run about $3.40 to $5.95 per sq ft, so a 1,503 sq ft roof is roughly $5,100 to $8,900. Materials are typically $130 to $160 per square, labor $300 to $500 per square, and tear-off $100 to $200 per square.
What slope can asphalt shingles go on?
Asphalt shingles are allowed on slopes of 2/12 or steeper under the International Residential Code. Below 2/12 you need a low-slope membrane system, not shingles.
Do I need underlayment and ice and water shield?
Yes. Underlayment goes under the shingles across the whole roof, and ice and water shield goes at the eaves, valleys and around penetrations in cold climates. This calculator counts underlayment rolls; ask your roofer about shield coverage for your area.
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