February 1, 2023

How to Calculate Roof Waste Factor

Learn how to calculator waste factor, and what popular waste percentages are used in roofing.

Time to read:
2 Minutes
Written by
Kate Robertson


When it comes to roofing, determining the waste factor is a crucial step that directly impacts the overall cost of the project. The waste factor is essentially the amount of extra material needed to account for cuts, overlaps, and mistakes during the installation process. In this blog post, we will discuss how to determine the waste factor when roofing to ensure that you have enough materials for the job without overspending.

Understanding Waste Factor

The first step in determining the waste factor is to understand what it is and how it is calculated. Generally, the waste factor for roofing is estimated to be around 10% to 15% of the total material needed for the project. This percentage may vary based on the type of roofing material, the complexity of the roof design, and the experience level of the installer.

To calculate the waste factor for your specific project, you should consider the following factors:

Roof size and design

Type of roofing material

Roof pitch and slope

Desired aesthetic and functional features

Experience level of the installer

Calculating Waste Factor

Once you have a clear understanding of the factors that can impact the waste factor, you can start to calculate it for your project. To do so, you will need to measure the roof accurately, taking into account any unique features such as skylights or chimneys. You should also consider the type of roofing material you plan to use, as different materials may require different amounts of waste.

To calculate the waste factor, you can use the following formula:

Total square footage of the roof x waste factor percentage = Total waste factor

For example, if the total square footage of your roof is 2,000 square feet, and you estimate a 10% waste factor, the total waste factor would be 200 square feet. This means you should order 2,200 square feet of material to complete the project.

There’s any easier way to calculate roof waste! Roofr offers waste recommendations on our Roofr Reports (on $10-$15 each). Your first report is free! Learn more about Roofr Reports.


Determining the waste factor when roofing is an essential step in ensuring that your project is completed within budget and on time. By understanding the factors that impact the waste factor and using the appropriate calculations, you can accurately estimate the amount of material needed for your project. If you are unsure about how to calculate the waste factor for your specific project, consider consulting with a roofing professional to ensure that your estimates are accurate.

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