Roofing Calculator

Easily estimate the surface area of your roof and determine how much roofing material you’ll need for your project. This calculator factors in the house base area, roof pitch, and slope correction to give you a more precise material estimate.

What Does the Roofing Calculator Do?

This tool helps you estimate:

• The actual area of a pitched roof (not just the footprint)
• The number of roofing squares required
• Roofing material quantities based on pitch correction

If your house base is irregular in shape, consider using our Area Calculator first to break it into simpler geometric shapes, then sum those areas to input into the Roofing Calculator.

Understanding Roof Pitch and Its Impact

Roof pitch (also called slope) measures how steep your roof is. It’s expressed as the vertical rise over 12 inches of horizontal run. For example, a roof with a 6/12 pitch rises 6 inches for every 12 inches of run.

Why Pitch Matters:

• Affects the actual roof area (steeper roofs have more surface area)
• Influences the type of roofing materials that can be used
• Impacts labor difficulty and cost
• Plays a key role in water drainage and snow load handling

Roof Pitch Correction Factor Table

Use the following pitch correction factors to adjust the horizontal roof area into the actual sloped surface area. Multiply your horizontal area by the matching correction factor from the table below:

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

Note: A steeply pitched roof (e.g., 24/12) has more than double the surface area of a flat one. Be sure to use the proper correction factor for each section of your roof to avoid over- or underestimating material needs.

Common Roofing Materials & Lifespan

Here are a few common roofing types used in residential construction and their typical lifespans:

• Asphalt Shingles: 15–30 years
• Membrane Roofing: 5–15 years
• Clay or Ceramic Tiles: 50–100+ years

Material choice will impact both the cost and the durability of your roof. Consider the local climate and your long-term maintenance preferences when selecting roofing materials.

Tips for Accurate Roofing Estimates

• Break complex roof shapes into simpler rectangles or triangles for measurement
• Always include overhangs or eaves if applicable
• Consider extra materials for waste, overlaps, and starter rows (typically 10–15% more)

Read more guideline here:

• NRCA (National Roofing Contractors Association)
• Owens Corning Roofing Learning Center
• GAF Roofing Guides

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