Roofing Calculator
Estimate Roof Area & Material Requirements
Total Roof Area
sq ft (Includes Pitch Correction)
Understanding Roof Pitch & Material Estimations
Calculating the exact area of a roof is necessary to estimate the amount of materials (such as shingles or membrane) required to construct it. However, because roofs are angled, you cannot simply use the flat square footage of your home's foundation. The true area is affected heavily by the steepness of the roof, known as its pitch.
Complex Shapes & Eaves
Our calculator estimates total roof area from your house's base footprint by assuming a standard square foundation and adding the length of the eaves (overhang). However, if your home has a complex layout with multiple dormers or intersecting rooflines, the most accurate method is to measure each individual geometric plane, calculate their area, and add them together.
Roofing Materials
Roofing materials are typically measured and sold in "Squares". One roofing square equals exactly 100 square feet. Asphalt shingles are usually bundled so that 3 bundles equal 1 square.
- Shingles: 15-30 year lifespan
- Membrane: 5-15 year lifespan
- Ceramic Tile: 100+ year lifespan
What is Roof Pitch?
Roof pitch is the measurement of a roof's vertical rise divided by its horizontal run. In the United States, a standard run of 12 inches (1 foot) is used. Therefore, pitch is measured as the rise of the roof over 12 inches. For example, a 7/12 roof pitch means that the roof rises 7 vertical inches for every 12 horizontal inches.
Outside of the U.S., a simple degree angle is typically used to represent the slope. Pitch is a determining factor for the cost of the roof, walkability, drainage, and material choices. Homes in areas of high rain or snowfall tend to feature much steeper pitches to shed water quickly.
The Slope Correction Factor
Because a sloped roof acts as the hypotenuse of a triangle, its actual surface area is greater than the flat area beneath it. To find the true surface area, you must multiply the flat horizontal area by a "correction factor" derived from the pitch. For very steep roofs (like an A-frame at 24/12), the correction multiplier can be greater than 2.0!
Typical Slope Correction Factors
The following table demonstrates how roof pitch and slope angle correspond to the mathematical multiplier used to determine true surface area.
| 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 |
| Pitch | Angle | Multiply By |
|---|---|---|
| 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 |