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. When measuring roof area, include the area covered by the eaves, which project beyond the side of the house. The "House Base Area"" is the area of land that the house covers, and for more complex shapes, can be estimated using the Area Calculator. Roof pitch is the measure of the steepness of a roof (rise/span), and can be estimated using the images below.
Roofing Area Calculator

Roofing Material Calculator

References:
The calculated area is only an estimation. In cases where a roof has a complex shape, such as in the image to the right, measuring the dimensions and areas of each part of the roof to calculate 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 1530 years, while membrane roofs usually last 515 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 span. It is often compared to slope, but is not exactly the same. In the United States, a span 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 US, a degree angle is typically used.
Roof pitch is a determining factor for 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 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 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 