To find how many bags of cellulose insulation your attic needs, divide your attic floor area by the coverage per bag for your target R-value. That coverage is printed on the bag chart. For one common 30-pound cellulose product, R-49 covers about 16.5 square feet per bag. That’s about 60 bags per 1,000 square feet, or roughly 73 bags for a 1,200 square foot attic with nothing in it. If you already have some insulation, you need fewer.
Every brand’s chart is a little different, so the method matters more than any one number. Our Grizzly Insulation Co teams blow cellulose into Denver attics all the time, so here’s the exact way we count bags.
What Do You Need to Calculate Cellulose Bags?
Two numbers and the bag chart. You need your attic floor area in square feet and the R-value you’re aiming for. The chart on the bag tells you how many square feet one bag covers at each R-value.
To get the area, measure the length and width of the attic floor and multiply. For a simple rectangle, 40 feet × 30 feet = 1,200 square feet. Our blog on how much insulation an attic needs helps you pick a target.
How Do You Read a Cellulose Bag Chart?
Find your R-value row, then read across. Here’s part of the attic chart from one GreenFiber stabilized cellulose fact sheet, for 30-pound bags:
R-value
Installed thickness
Settled thickness
Max coverage per bag
Bags per 1,000 sq ft
R-30
8.9 in
8.3 in
31.1 sq ft
32.2
R-38
11.2 in
10.4 in
22.8 sq ft
43.9
R-49
14.3 in
13.3 in
16.5 sq ft
60.5
R-60
17.3 in
16.1 in
13.0 sq ft
77.1
The chart warns not to exceed the maximum coverage per bag. Both the bag count and the installed thickness have to be met to reach the R-value.
How Many Cellulose Bags Does a 1,200 Square Foot Attic Need?
Divide the area by the coverage. Using the chart above:
R-38: 1,200 ÷ 22.8 = about 53 bags.
R-49: 1,200 ÷ 16.5 = about 73 bags.
R-60: 1,200 ÷ 13.0 = about 93 bags.
Round up, and add a couple of extra bags for the corners and around the hatch. Check our R49 insulation guide for what that depth looks like.
How Do You Count Bags If You Already Have Insulation?
Subtract what’s there. Measure your existing insulation and estimate its R-value. Old fiberglass runs about R-2.5 to R-3 per inch, so 6 inches is roughly R-15 to R-18. Then calculate bags only for the R-value you’re adding.
For example, to go from about R-19 to R-49 in a 1,200 square foot attic, you’d add about R-30. That’s 1,200 ÷ 31.1 = about 39 bags. Our blog on whether to remove old insulation first explains when the old layer can stay.
Do Walls Use the Same Cellulose Bag Chart as Attics?
Walls get dense-packed at a much higher density, around 3.5 pounds per cubic foot, so they use a separate chart. A 2×4 wall needs roughly three-quarters of a pound per square foot of wall.
Attic charts assume a fluffier loose fill that sits on the floor. Always use the attic section of the chart for attics and the wall section for walls. Our guide on what blow-in insulation is explains the difference.
What R-Value Should a Denver Attic Have?
R-49 to R-60. New homes in climate zone 5, which includes Denver, need R-60 under the current energy code. For an existing Denver attic, R-49 is a solid, common target that gets you most of the benefit.
Does Cellulose Settle After It's Blown In?
A little. That’s why the chart lists an installed thickness and a slightly lower settled thickness. Crews should blow to the installed depth so the settled layer still hits the R-value.
You’ll hear that cellulose “loses half its R-value” as it settles. That one gets repeated a lot, but it has nothing behind it when the bag count is right. The chart already accounts for settling. If your attic were ours, we’d count bags as they go in, then check depth markers before calling it done. See the pros and cons of cellulose insulation for more.
Should You Air Seal Before Blowing Cellulose?
Gaps around lights, fans and pipes let warm air carry moisture into the insulation. Sealing them first makes every bag work harder. Our blog on what air sealing an attic involves shows where the leaks hide.
Also add a dam around the attic hatch so the cellulose stays put. See insulation dams.
Should You Rent a Blower or Hire a Pro?
For a small, easy attic, a rented blower and a helper can do it in a day. The hard part isn’t the blowing. It’s the air sealing, the baffles at the soffits and getting an even depth in tight corners near the eaves.
Many Denver attics have low roof pitches and lots of can lights, which makes DIY slow and messy. A crew with a truck-mounted machine can usually finish in a few hours. Our attic insulation service includes the air sealing, and our blog on types of attic insulation compares cellulose with the other options.
Count Your Bags of Cellulose Insulation the Right Way
Measure your attic, pick your R-value, read the bag chart and divide. Subtract what’s already there, add a couple of spare bags, and seal the leaks first. That’s all it takes to buy the right amount.
Rather have it done for you in your Denver home? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
How Many Bags of Cellulose Insulation Your Attic Needs
To find how many bags of cellulose insulation your attic needs, divide your attic floor area by the coverage per bag for your target R-value. That coverage is printed on the bag chart. For one common 30-pound cellulose product, R-49 covers about 16.5 square feet per bag. That’s about 60 bags per 1,000 square feet, or roughly 73 bags for a 1,200 square foot attic with nothing in it. If you already have some insulation, you need fewer.
Every brand’s chart is a little different, so the method matters more than any one number. Our Grizzly Insulation Co teams blow cellulose into Denver attics all the time, so here’s the exact way we count bags.
What Do You Need to Calculate Cellulose Bags?
Two numbers and the bag chart. You need your attic floor area in square feet and the R-value you’re aiming for. The chart on the bag tells you how many square feet one bag covers at each R-value.
To get the area, measure the length and width of the attic floor and multiply. For a simple rectangle, 40 feet × 30 feet = 1,200 square feet. Our blog on how much insulation an attic needs helps you pick a target.
How Do You Read a Cellulose Bag Chart?
Find your R-value row, then read across. Here’s part of the attic chart from one GreenFiber stabilized cellulose fact sheet, for 30-pound bags:
The chart warns not to exceed the maximum coverage per bag. Both the bag count and the installed thickness have to be met to reach the R-value.
How Many Cellulose Bags Does a 1,200 Square Foot Attic Need?
Divide the area by the coverage. Using the chart above:
Round up, and add a couple of extra bags for the corners and around the hatch. Check our R49 insulation guide for what that depth looks like.
How Do You Count Bags If You Already Have Insulation?
Subtract what’s there. Measure your existing insulation and estimate its R-value. Old fiberglass runs about R-2.5 to R-3 per inch, so 6 inches is roughly R-15 to R-18. Then calculate bags only for the R-value you’re adding.
For example, to go from about R-19 to R-49 in a 1,200 square foot attic, you’d add about R-30. That’s 1,200 ÷ 31.1 = about 39 bags. Our blog on whether to remove old insulation first explains when the old layer can stay.
Do Walls Use the Same Cellulose Bag Chart as Attics?
Walls get dense-packed at a much higher density, around 3.5 pounds per cubic foot, so they use a separate chart. A 2×4 wall needs roughly three-quarters of a pound per square foot of wall.
Attic charts assume a fluffier loose fill that sits on the floor. Always use the attic section of the chart for attics and the wall section for walls. Our guide on what blow-in insulation is explains the difference.
What R-Value Should a Denver Attic Have?
R-49 to R-60. New homes in climate zone 5, which includes Denver, need R-60 under the current energy code. For an existing Denver attic, R-49 is a solid, common target that gets you most of the benefit.
Does Cellulose Settle After It's Blown In?
A little. That’s why the chart lists an installed thickness and a slightly lower settled thickness. Crews should blow to the installed depth so the settled layer still hits the R-value.
You’ll hear that cellulose “loses half its R-value” as it settles. That one gets repeated a lot, but it has nothing behind it when the bag count is right. The chart already accounts for settling. If your attic were ours, we’d count bags as they go in, then check depth markers before calling it done. See the pros and cons of cellulose insulation for more.
Should You Air Seal Before Blowing Cellulose?
Gaps around lights, fans and pipes let warm air carry moisture into the insulation. Sealing them first makes every bag work harder. Our blog on what air sealing an attic involves shows where the leaks hide.
Also add a dam around the attic hatch so the cellulose stays put. See insulation dams.
Should You Rent a Blower or Hire a Pro?
For a small, easy attic, a rented blower and a helper can do it in a day. The hard part isn’t the blowing. It’s the air sealing, the baffles at the soffits and getting an even depth in tight corners near the eaves.
Many Denver attics have low roof pitches and lots of can lights, which makes DIY slow and messy. A crew with a truck-mounted machine can usually finish in a few hours. Our attic insulation service includes the air sealing, and our blog on types of attic insulation compares cellulose with the other options.
Count Your Bags of Cellulose Insulation the Right Way
Measure your attic, pick your R-value, read the bag chart and divide. Subtract what’s already there, add a couple of spare bags, and seal the leaks first. That’s all it takes to buy the right amount.
Rather have it done for you in your Denver home? Grizzly Insulation Co can help. We’re BPI Certified and an Xcel Energy rebate partner.
Call (303) 854-6221, or check our blown-in insulation service.
Frequently Asked Questions
About 60 bags of a 30-pound product, based on one common chart.
It depends on the R-value. For R-38, about 23 square feet per bag on one common chart.
No. Always use the chart on the bags you buy.
Yes, if the fiberglass is dry and clean.
Yes. Many stores lend one with a bag purchase.