May 24, 2024

How to Calculate Roof Waste Factor

Learn how to calculator waste factor, and what popular waste percentages are used in roofing. Plus, get our free waste factor worksheet.

Time to read:
2 Minutes
Written by
Jennifer Cote

When it comes to roofing, determining the waste factor is a crucial step that directly impacts the overall cost of the project. This guide will walk you through how to calculate waste factor. Or, use our FREE worksheet at the bottom of the page that will calculate it for you!

What is waste factor in roofing?

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.

What impacts waste in a roofing job?

Generally, the waste factor for roofing is estimated to be around 10% to 15% of the total material needed for the project.

But that number can go up or down depending on a few things:

Roof Complexity: The more complex the roof design, the higher the waste factor. Roofs with multiple valleys, hips, dormers, and other architectural features require more cuts and adjustments, leading to more waste.

Material Type: Different roofing materials have varying waste factors. For example, asphalt shingles generally have a lower waste factor compared to metal roofing or tiles because they are easier to cut and fit.

Installer Experience: Experienced roofers tend to manage materials more efficiently, resulting in lower waste. Conversely, less experienced installers might make more errors, increasing the waste factor.

Roof Slope: Steeper roofs can lead to higher waste because of the difficulty in handling and installing materials at steep angles. Additionally, certain roofing materials may slide or shift more on steeper slopes, leading to more waste.

Weather Conditions: Adverse weather conditions such as high winds, rain, or extreme heat can damage materials or make them harder to handle, increasing waste.

Waste Calculator

There are a few simple steps to calculate roofing waste. Here’s a basic method to estimate your waste:

1. Measure the Roof Area: Measure the total area of your roof in square feet. Make sure to take into account any unique features such as skylights or chimneys.

2. Determine the Waste Percentage: This will depend on the complexity, material type, and other factors. This chart can help you determine waste expectancy, but it'll differ based on those other factors.

roofing waste factor chart

3. Calculate Waste: Multiply the roof area by the waste factor (WF) percentage to find the additional material needed.


WF=Roof Area×(Waste Percentage/100)

For example, if your roof area is 2,000 square feet and you have a WF of 10%, the calculation would be:

WF=2000×(10/100)=200 square feet

So, you should purchase 2,200 square feet of roofing material to account for waste.

Waste factor calculator worksheet

Use this free worksheet to view our waste factor chart. It has a free roof waste calculator built in, too.

Roofr's automatic waste calculation

Roofr report with waste factor calculated

Did you know that Roofr's measurement reports calculate roofing waste for you? Book a demo with our team to see Roofr in action.

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