Roofing Calculator
The following tools estimate the area of a roof, as well as the amount of materials necessary to construct a roof of a given area. The "House Base Area" is the area of land that the house covers, and for more complex shapes, it can be estimated using the Area Calculator.
Roofing Area Calculator
Roofing Material Calculator
The calculated area is only an estimation. In cases where a roof has a complex shape, measuring the dimensions and areas of each part of the roof to calculate the total area will result in a more accurate measurement of area. The calculator cannot account for complex shapes based on a measurement of square footage alone. The Area Calculator can be used to calculate the area of a variety of simple shapes that together can comprise the area of the roof. Using the aggregate area of these simple shapes can yield a more accurate roof area to be used with the Roofing Material Calculator.
The most common roofing materials used in the United States include shingles, membrane roofing, and ceramic tile, all of which have different life spans. Shingle roofs typically have a life span of 15-30 years, while membrane roofs usually last 5-15 years. Although ceramic tile roofs are expensive, they can have a life span of over 100 years.
Roof Pitch
Roof pitch is the measurement of a roof's vertical rise divided by its horizontal run. It is often compared to slope, but is not exactly the same. In the United States, a run of 12 inches (1 foot) is used, and pitch is measured as the rise of the roof over 12 inches. For instance, a 7/12 roof pitch means that the roof rises 7 inches for every 12 horizontal inches. Outside of the U.S., a degree angle is typically used.
Roof pitch is a determining factor for the cost of the roof, as well as the roof area, and the type of materials used. It affects walkability as well as drainage, and roofs in areas of high rain or snowfall tend to have steeper pitches.
Roof pitch affects the actual area of the roof. Depending on whether the roof area is measured horizontally (possibly from a drawing or photograph), a correction factor is necessary to determine the actual area of the roof. Given pitch and a horizontal area measurement, multiply the horizontal area by a correction factor corresponding to pitch, provided in the table below, to determine the actual area of the roof to be used in the Roofing Material Calculator. While it is possible to estimate the amount of necessary materials using only the total roof area measurement, as can be seen from the table, depending on how large the pitch of the roof, the actual area of the roof can differ by up to 2.236 from the measured total area at a pitch of 24/12. As such, while it can be cumbersome, measuring the area and pitch of each part of the roof and multiplying by the corresponding correction factor will result in the most accurate estimate of necessary roofing materials.
Typical Slope Correction Factors:
| Pitch | Angle | Multiply By | Pitch | Angle | Multiply By |
|---|---|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 2/12 | 9.5° | 1.014 |
| 3/12 | 14.0° | 1.031 | 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 | 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 | 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 | 10/12 | 39.8° | 1.302 |
| 11/12 | 42.5° | 1.357 | 12/12 | 45.0° | 1.414 |
| 13/12 | 47.3° | 1.474 | 14/12 | 49.4° | 1.537 |
| 15/12 | 51.3° | 1.601 | 16/12 | 53.1° | 1.667 |
| 17/12 | 54.8° | 1.734 | 18/12 | 56.3° | 1.803 |
| 19/12 | 57.7° | 1.873 | 20/12 | 59.0° | 1.944 |
| 21/12 | 60.3° | 2.016 | 22/12 | 61.4° | 2.088 |
| 23/12 | 62.4° | 2.162 | 24/12 | 63.4° | 2.236 |
Frequently Asked Questions
How does the Roofing Area Calculator estimate the roof area?
It starts from the house base area, extends the footprint to account for the eaves sticking out past the walls, and then multiplies by a slope correction factor: the square root of 1 + (pitch/12) squared for a pitch, or 1 divided by the cosine of the angle for a degree angle. Steeper roofs have noticeably more surface than the land they cover.
What is a roofing square?
A roofing square is 100 square feet of roof area. Roofing materials are estimated per square: about 3 bundles of composition shingles cover one square, one roll of roll roofing covers about one square, and the felt rolls cover roughly 4 squares (#15 felt) or 2 squares (#30 felt) each. The calculators round every material up to whole units and include a 10% buffer in the square count for cuts and waste.
Why does the estimate include a 10% buffer?
Real roofs need extra material for cuts at hips, valleys, and edges, starter strips, ridge caps, and the occasional damaged piece. Ordering about 10% more than the bare area is the standard rule of thumb so the job does not stall waiting for one more bundle.