Roofing calculator: how big is my roof?
Pitch, roof area, squares and shingle bundles. Free, no sign-up, nothing leaves your browser.
Type the pitch and your measurements to see the roof area.
1 square = 100 sq ft of roof
Add a section below to get the roof area.
Each line is rounded on its own. The total adds the unrounded areas, so the lines can be off from it by a few hundredths.
Not counted here: starter strip, hip and ridge caps, drip edge, flashing, ice and water barrier, fasteners and vents.
Clear every section, the pitch and the shingle figures?
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Confirm the measurements with your roofer or supplier before you order.
Section __K__
How were these measured?
Flat: taken on the ground or off a plan, looking straight down. These get the slope factor once. Along the roof: figures already taken on the slope, like a measurement report. Never multiplied again.
Feet and inches as 40' or 12' 6". A plain 12.5 means twelve and a half feet, and 10.10 means 10.1 ft, not 10' 10".
If this part of the roof has a different pitch, like a porch roof, give it its own. Only this section uses it.
Take them off the plans, in any one unit: 7' 6" over 15' is 6 in 12. The run is the level distance, not the length of the slope.
Do the length and width reach the roof edge?
Walls measured on the ground stop at the wall, and the roof doesn't. Choose wall to wall to add how far it sticks out, measured level.
Overhang past the ends of the length
On a gable roof with the ridge along the length, these are the gable ends. An end that meets a wall or another section has none.
Overhang past the sides of the width
On a gable roof with the ridge along the length, these are the eaves. A side that meets a wall or another section has none.
The area you won't shingle, as roof surface. A skylight 2 ft by 4 ft is 8 sq ft. It comes off after the slope factor.
How the roofing calculator works
Every section starts with one question: where did these numbers come from? Measured flat means you took them on the ground or off a plan, looking straight down, and they get the slope factor once. Measured along the roof means someone already took them on the slope, the way a measurement report does, so they're never multiplied again. Mix the two up and the roof comes out wrong in either direction. Multiply a slope figure a second time and a 6/12 roof grows by nearly 12%. Skip the factor on a flat one and it shrinks by about a tenth.
The pitch is one value, however you write it. Type it the way you have it: 6 in 12, a rise and run off the plans, or an angle. The other two forms and the slope factor show up right under it. The calculator uses your number exactly as typed, so 26.57 degrees is a hair steeper than 6/12. On the example house that hair is worth 0.06 sq ft. At 27 degrees it's worth 5.41.
Overhang goes on before the factor, because walls stop at the wall and the roof doesn't. If you measured wall to wall, the calculator asks how far the roof sticks out, measured level, and on how many edges. It adds that to the length and width, then multiplies. Skylights and chimneys come off afterward, as roof area.
Squares are the roof area divided by 100, kept to two decimals and never rounded up. Bundles get rounded once, at the very end: the area plus your allowance, divided by the coverage on the wrapper, then up to the next whole bundle. Underlayment rolls work the same way, with their own extra for laps.
A hip roof doesn't have to be cut into triangles. When every plane shares one pitch and none overlaps another seen from above, the whole roof is its outline from above times one slope factor, because each plane's area is its own flat area times that same factor. Save sections for the parts that differ, like a shallower porch, an addition, or an outline that isn't one rectangle.
Who this is for
You've got a roofing quote that says 17 squares, for a house you know as 1,120 square feet, and you'd like to know whether those two numbers belong together. Or you're the roofer, with the plans on the tailgate and a supplier order to place.
Either way, you type what you already have: wall lengths taken on the ground, the overhang, the pitch off the quote or the plans, the figure printed on the bundle wrapper. Nobody has to go up on the roof for any of it.
If you're the roofer, you already know this one. Federal rules require fall protection for employees working 6 feet or more above a lower level in residential construction, so the numbers you can get from the ground and the plans are the cheap ones. Check them here first.
We don't put a price on a roof here. Only quotes from roofers who've seen yours can do that.
Homeowner and roofer questions about roof pitch and squares
How do I calculate roof square footage?
Measure the footprint from the ground, add the overhang, then multiply by the slope factor for your pitch. A house 40 by 28 ft with a 1 ft overhang all around is 42 by 30, or 1,260 sq ft seen from above. At 6/12 the factor is 1.118034, so the roof is 1,408.72 sq ft. A porch with a different pitch gets a section of its own.
Is roof square footage the same as my house's square footage?
No, and the roof is usually the bigger one. It covers the footprint plus the overhang, and the slope stretches every foot of it. That 40 by 28 ft house is 1,120 sq ft of floor and 1,408.72 sq ft of roof, about 26% more. A two-story house turns it around: the roof covers one floor's footprint, not both floors.
How many squares is my roof?
Divide the roof's surface area by 100. The example house with its porch comes to 1,507.68 sq ft, which is 15.08 squares. Keep the two decimals and don't round up yet: the rounding belongs at the end, on whole bundles. If a quote says 17 squares for that roof, it sits 12.8% above the measured area. Waste, starter and ridge shingles, and whole bundles can account for that.
What is a square in roofing?
100 square feet of roof surface. It's a trade unit: NIST's handbook of units lists "1 square (building)" as 100 square feet. Shingles are packed and priced by it, which is why a quote talks in squares while the wrapper talks in bundles per square or square feet per bundle.
What is a 6/12 roof pitch in degrees?
26.57 degrees. A 6/12 roof rises 6 inches for every 12 inches of level run, and the angle is the arctangent of 6 divided by 12. Its slope factor is 1.118034, so every 12 inches of level run is 13.42 inches of roof. The roof pitch chart lists every whole pitch from 1/12 to 24/12.
What is a roof pitch multiplier?
It's the slope factor: the number that turns an area seen from above into the area on the slope. Take the pitch as rise over run, square it, add 1 and take the square root. At 6/12 that's the root of 1.25, or 1.118034. Multiply only areas that were measured flat. A measurement report's areas are already on the slope.
How do I find my roof's pitch without going up there?
Look on paper first: the quote, a measurement report, the house plans or the truss drawings. Pitch is usually written as 6/12 or 6:12. Plans may give a rise and a run instead, say 7 ft 6 in of rise over a 15 ft run. Type those under Rise and run and you get 6 in 12. You won't need a ladder for any of that.
How do I measure a hip roof from the ground?
Measure the walls, the overhang and the pitch, then treat the whole roof as one rectangle. When every plane has the same pitch and none overlaps another seen from above, the roof is its outline from above times one slope factor. A 48 by 30 ft house with an 18 in overhang all around at 5/12 is 51 by 33 ft, times 13/12: 1,823.25 sq ft. You don't need a single triangle.
How many bundles of shingles are in a square?
It depends on the shingle, and that's why the calculator asks for the wrapper's figure. GAF's installation instructions say three bundles of its Timberline HDZ line cover 98.4 sq ft, four bundles of Camelot II cover 100.6, and five of Grand Sequoia cover 100. Type what your wrapper says, in either form, and it's used exactly as printed.
How many bundles of shingles do I need for 1,500 square feet?
First make sure 1,500 is the roof, not the house. If it's the roof surface, add your allowance, divide by the wrapper's coverage and round up once. If your wrapper says 32.8 sq ft per bundle, that's 1,500 divided by 32.8, or 45.73, so 46 bundles before any allowance. A wrapper that instead says 3 bundles per square gives exactly 45.
How many rolls of underlayment do I need?
Divide the roof area plus your extra by the roll's coverage. FeltBuster's 1,000 sq ft excludes laps. For standard installation at 4/12 or steeper, GAF specifies 3 in side laps and 6 in end laps. On its 48 in roll, side laps alone need about 6.7% extra per roof area, before end laps. From 2/12 to under 4/12, its double coverage uses 22.5 in exposure; 100% extra can still fall short. Confirm the count with your roofer, especially for low slopes or special rain/snow installation.
Roof pitch chart: degrees and slope factor
Here's every whole pitch from 1/12 to 24/12, worked out with the same formulas the calculator uses. A footprint isn't a roof: at 12/12, a thousand square feet seen from above is 1,414 sq ft of roof. Being one step off on the pitch matters as well. Type 7/12 for a 6/12 roof and you've added about 3.5%.
| Pitch | Angle | Slope factor | 1,000 sq ft measured flat becomes |
|---|---|---|---|
| 1/12 | 4.76 degrees | 1.003466 | 1,003 sq ft |
| 2/12 | 9.46 degrees | 1.013794 | 1,014 sq ft |
| 3/12 | 14.04 degrees | 1.030776 | 1,031 sq ft |
| 4/12 | 18.43 degrees | 1.054093 | 1,054 sq ft |
| 5/12 | 22.62 degrees | 1.083333 | 1,083 sq ft |
| 6/12 | 26.57 degrees | 1.118034 | 1,118 sq ft |
| 7/12 | 30.26 degrees | 1.157704 | 1,158 sq ft |
| 8/12 | 33.69 degrees | 1.20185 | 1,202 sq ft |
| 9/12 | 36.87 degrees | 1.25 | 1,250 sq ft |
| 10/12 | 39.81 degrees | 1.301708 | 1,302 sq ft |
| 11/12 | 42.51 degrees | 1.356568 | 1,357 sq ft |
| 12/12 | 45.00 degrees | 1.414214 | 1,414 sq ft |
| 13/12 | 47.29 degrees | 1.474317 | 1,474 sq ft |
| 14/12 | 49.40 degrees | 1.536591 | 1,537 sq ft |
| 15/12 | 51.34 degrees | 1.600781 | 1,601 sq ft |
| 16/12 | 53.13 degrees | 1.666667 | 1,667 sq ft |
| 17/12 | 54.78 degrees | 1.734054 | 1,734 sq ft |
| 18/12 | 56.31 degrees | 1.802776 | 1,803 sq ft |
| 19/12 | 57.72 degrees | 1.872684 | 1,873 sq ft |
| 20/12 | 59.04 degrees | 1.943651 | 1,944 sq ft |
| 21/12 | 60.26 degrees | 2.015564 | 2,016 sq ft |
| 22/12 | 61.39 degrees | 2.088327 | 2,088 sq ft |
| 23/12 | 62.45 degrees | 2.161854 | 2,162 sq ft |
| 24/12 | 63.43 degrees | 2.236068 | 2,236 sq ft |
Sources and last checked
- Units: NIST Handbook 44 (2026), Appendix C, General Tables of Units of Measurement. 1 ft = 0.3048 m and 1 in = 2.54 cm, exactly; 1 sq ft = 0.09290304 sq m; "1 square (building)" = 100 square feet.
- Bundle coverage examples: GAF installation instructions for Timberline HDZ and related shingles (RESTL622, 2023), Camelot II (updated September 2025) and Grand Sequoia.
- Underlayment example: GAF FeltBuster data sheet (2025, RESUL183-0125) and installation instructions (2019).
- Fall protection: 29 CFR 1926.501(b)(13), residential construction (eCFR).
- Pitch chart: computed from the formulas in How the roofing calculator works.
Last checked: October 8, 2026 (dataset version 2026-10-07).
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