Calculating roof waste factor can be a real pain. Good thing our quick how-to guide and easy roof waste calculator are here to help.
When you’re quoting a roofing job, determining waste factor is VITAL. It directly impacts the total cost of the project, so getting it wrong can cost you in profit, time, and reputation.
Keep reading for the low-down on how to calculate waste factor. Then use our FREE worksheet at the bottom of the page to calculate it for you.
Or do you want it just… solved for you instead?
Roofr users get accurate, affordable roof measurement reports in as little as two hours. Waste factor included.
Talk to our team to see it in action. (You’ll never worry about measurements again.)
What is waste factor in roofing?
The waste factor of any roofing job is the amount of extra material needed. That means accounting for cuts, overlaps, and mistakes during installation.
An accurate waste factor ensures you have enough materials without overspending. Staying on budget means proper profit margins, happier customers, and a smoother experience.
Figuring the waste factor out means asking a few questions.
- How big is the job?
- How experienced is your team?
- How tricky is the roof?
It might take some practice to get a consistent roof waste factor calculation dialed in. But taking the time to figure it out is worth it. So let’s get you there.
Tip: Hiding your waste factor in big pricing blocks isn’t best practice. Be transparent on your proposals, with itemized quotes that break everything down for the customer. It’s a bit more work upfront, but it builds relationships of trust.
What impacts waste in a roofing job?
In general, a solid roofing waste factor estimate is around 10% to 15% of the total material needed for the project.
That’s your starting point. But that number will go up or down depending on many factors:
- Roof complexity - The more complex the roof design, the higher the waste factor. Roofs with a lot of valleys, hips, dormers, and other architectural features need more adjustments. That means more off-cuts left over.
- Material type - Some roofing materials make more waste. Asphalt shingles generally have a lower waste factor compared to metal roofing or tiles — easier to cut and fit. There may even be a difference between specific products or brands, so lean on your expertise here.
- Installer experience - Roofers with years of experience are more efficient, making less waste. Your younger guys will make more mistakes, especially when they’re first starting out. That’s fine while they learn the ropes, but factor it in.
- Roof slope - Steeper roofs usually mean more waste. It’s a lot tougher to handle and install materials at those sharp angles. Plus, some roofing materials will slide or shift more on steep slopes, so watch for that.
- Weather conditions - Bad weather conditions like high winds, heavy rain, and extreme heat are harder to work in. Higher risk of damaged materials, more waste. It’s not easy to plan for this one. You may even include a “bad weather” price disclaimer on proposals if you’re working in a hot spot during storm season.
Lesson is, don’t treat every roof the same. If you quote the same waste factor on every job, you’re asking for trouble. Customers pay attention and hate paying more, especially if it’s avoidable or unjustified.
If you quote a low waste factor but make a mountain of garbage (and try to charge the customer more for it), that leads to confusion. Anger. A bad review. Less future work.
It’s better to estimate too high than too low, but even then, you could lose work to competitors with more accurate pricing. So don’t risk it.
Calculating roof waste factor
You are the expert of your roofing business! So you probably want to understand the math yourself first before blindly relying on a roof waste calculator. That way, you can tweak it for your own personal situation and know what to adjust in the future.
Once you have it down, though, definitely put an easy-to-repeat process in place. Tech tools like Roofr’s measurement reports make it a breeze.
Here’s a basic method to estimate your waste:
1. Measure the Roof Area: Measure the total area of your roof in square feet. Take into account unique features like skylights or chimneys. (Or just use our instant estimator.)
2. Find a Waste Percentage: This is the part that depends on the factors we listed above, so it’s specific to each roofing job. Calculating this gets easier the more you do it. Use this waste expectancy chart as a starting point:
3. Calculate Waste: Multiply the roof area by the waste factor (WF) percentage to find the extra material needed.
Formula:
WF=Roof Area×(Waste Percentage/100)
For example, if your roof area is 2,000 square feet and you have a WF of 10%, your calculation would be:
WF=2000×(10/100)=200 square feet
So in total, you'd buy 2,200 square feet of roofing material to account for waste.
Done. Though of course, this gets more complicated with bigger jobs.
Your roof waste calculator worksheet
Use this free worksheet to view our waste factor chart.
It has a free roof waste calculator built in, too.
Don’t worry, it’s not behind a wall or anything. It’s hosted on Google Sheets, so it’s dead simple to use in your browser. Or, download as a .xlsx to use in Excel.
Roofr does automatic waste calculation
Now that you’ve got the basics, let’s zoom out a bit. If you’re running lean, it’s not sustainable to manually calculate waste factor every time. It’s got to be built into your process.
If you hate wasted time as much as wasted roofing material, check it out:
Roofr's measurement reports calculate roofing waste for you. They’re some of the fastest, most affordable reports in the industry. And once our users try them, they never go back.