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.
Understanding Roof Area and Measurements
The calculated area provided by standard formulas is an estimation. In cases where a roof has a complex shape (multiple gables, dormers, or valleys), measuring the dimensions and areas of each part of the roof to calculate the total area will result in a more accurate measurement. The calculator cannot account for complex shapes based on a measurement of the house's square footage alone. You can calculate the area of simple shapes that comprise the roof and aggregate them to yield a more accurate total area.
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 lifespan of 15-30 years, while membrane roofs usually last 5-15 years. Although ceramic tile roofs are expensive, they can have a lifespan of over 100 years.
What is 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 as the constant base, and pitch is measured as the rise of the roof over those 12 inches. For instance, a 7/12 roof pitch means that the roof rises 7 inches vertically 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, the actual surface area, and the type of materials that can be used. It affects walkability during installation as well as drainage efficiency. Roofs in areas with high rain or snowfall tend to have steeper pitches.
Why Roof Pitch Affects Surface Area
Roof pitch affects the actual surface area of the roof. If you only measure the horizontal footprint of a house, you are not accounting for the slanted angle of the roof. A correction factor (multiplier) is necessary to determine the true surface area.
Given a pitch and a horizontal area measurement, you must multiply the horizontal area by a correction factor corresponding to the pitch (provided in the table below) to determine the actual area of the roof. As you can see from the table, depending on how steep the roof is, the actual area can differ significantly from the footprint—up to a 2.236 multiplier for a very steep 24/12 pitch.
Typical Slope Correction Factors (Multipliers)
| Pitch |
Angle |
Multiply Footprint By |
Pitch |
Angle |
Multiply Footprint By |
| 1/12 | 4.8° | 1.003 | 13/12 | 47.3° | 1.474 |
| 2/12 | 9.5° | 1.014 | 14/12 | 49.4° | 1.537 |
| 3/12 | 14.0° | 1.031 | 15/12 | 51.3° | 1.601 |
| 4/12 | 18.4° | 1.054 | 16/12 | 53.1° | 1.667 |
| 5/12 | 22.6° | 1.083 | 17/12 | 54.8° | 1.734 |
| 6/12 | 26.6° | 1.118 | 18/12 | 56.3° | 1.803 |
| 7/12 | 30.3° | 1.158 | 19/12 | 57.7° | 1.873 |
| 8/12 | 33.7° | 1.202 | 20/12 | 59.0° | 1.944 |
| 9/12 | 36.9° | 1.250 | 21/12 | 60.3° | 2.016 |
| 10/12 | 39.8° | 1.302 | 22/12 | 61.4° | 2.088 |
| 11/12 | 42.5° | 1.357 | 23/12 | 62.4° | 2.162 |
| 12/12 | 45.0° | 1.414 | 24/12 | 63.4° | 2.236 |