Blown-in Attic Insulation Cost Calculator
Calculate how much insulation you need in your attic and estimate the total cost of blown-in insulation. Enter your attic size and project details to get a quick and accurate estimate.
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How much does blown-in insulation cost for a 1,000 sq ft attic?
Blowing 12 inches of cellulose into a 1,000 sq ft attic (about R-42) takes roughly 51 bags, running around $900 in materials. The same depth in blown fiberglass (about R-30 at that depth) takes about 33 bags, closer to $700. Professionally installed, expect $1,750–$2,000 for the same attic once labor is included. Enter your own depth and square footage below for an exact number.
You need
51 bags
1,000 sq ft attic, cellulose, blowing to 12 in (R-42)
- Net depth being added12.0 in
- Resulting R-valueR-42
- DIY material cost$918
- Hiring a pro (est.)Not selected
In this guide
Why blown-in insulation is priced by depth, not just R-value
You may have already looked up your target R-value for your climate zone — that part's simple enough. But when you go to actually buy blown-in insulation, the bags don't ask for an R-value. They ask how deep you're blowing it, because depth is the number the blower operator (or the machine, if you're renting one) actually controls. R-value is just depth multiplied by the material's R-per-inch rating.
That distinction matters for cost, too. Two materials at the same R-value target can need very different bag counts, because they achieve that R-value at different depths and cover different square footage per bag. This calculator works the way the job actually gets priced — enter your desired depth, and it converts that straight into bags and dollars for either cellulose or fiberglass.
How depth determines bags and cost
The math behind every blown-in insulation bag count follows the same chain.
The depth-to-cost chain
- Pick your depth. Most attics target 12–19 inches, depending on material and climate zone — check our Attic Insulation Calculator if you want to work backward from a target R-value instead.
- Convert depth to R-value. Multiply inches by the material's R-per-inch rating — about 3.5 for cellulose, 2.5 for fiberglass.
- Convert R-value to bags. Manufacturer coverage charts state how many square feet one bag covers at a reference R-value. Scale that ratio to your actual target, then add 10–15% for settling and waste.
- Multiply by price per bag. That gives your DIY materials cost — compare it against a professional installed rate to see what labor is actually worth.
The calculator above runs this whole chain the moment you enter a depth — no need to look up your R-value first.
A worked example
Let's price out a 1,000 sq ft attic (40×25 ft), blowing in 12 inches of cellulose with no existing insulation.
Step-by-step
- Depth: 12 inches. R-value achieved: 12 × 3.5 = R-42.
- Reference coverage: cellulose covers about 50 sq ft/bag at R-19.
- Bags needed: (1,000 ÷ 50) × (42 ÷ 19) = 20 × 2.21 ≈ 44.2 bags before waste.
- Add 15% settling allowance: 44.2 × 1.15 ≈ 51 bags.
- At $18/bag: 51 × $18 = $918 in materials.
Switch that same 12-inch depth to fiberglass instead, and you'd get about R-30 (2.5 R/inch × 12) instead of R-42, using roughly 33 bags at a typical $18–22 price point — around $700. Fiberglass reaches a lower R-value at the same depth, but needs fewer bags to do it, since it covers more area per bag at any given R-value.
Cellulose vs. fiberglass for blowing
What if you're deciding between the two purely on cost and performance, not just what's on the shelf? Here's how they actually compare when blown.
| Factor | Blown cellulose | Blown fiberglass |
|---|---|---|
| R-value per inch | ~3.5 | ~2.5 |
| Depth for R-49 | ~14 inches | ~19.6 inches |
| Material cost per sq ft | $0.80–$1.50 | $0.70–$1.30 |
| Moisture behavior | Absorbs moisture, can lose R-value if wet | Doesn't absorb moisture, dries out faster |
| Settling | Settles more — needs a bigger waste allowance | Settles less over time |
Know your depth? Get your exact bag count and cost.
Run the numbers in the calculator above →DIY materials vs. hiring it out
What if you're weighing whether to rent a blower yourself? DIY materials for our 1,000 sq ft example run $700–$920 depending on material. A professional installed job for the same attic typically runs $1.00–$3.00 per square foot including labor — $1,750–$2,000 at a mid-range $1.75–2.00/sq ft rate. That gap is almost entirely labor and equipment, since most home improvement stores rent blower machines free with a bulk bag purchase.
What tips the decision toward hiring it out? Attics with tight, hard-to-access spaces, extensive existing insulation that needs assessment first, or any sign of moisture or pest damage are all situations where a professional's experience is worth paying for — a DIY blower job in a cramped attic with poor visibility often ends up thinner and less even than a pro's.
Common mistakes to avoid
- ✕Assuming the same depth gives the same R-value across materials. 12 inches of cellulose and 12 inches of fiberglass are not equivalent — always check R-per-inch before comparing.
- ✕Buying bags based on the depth marker on the blower hose alone. Blower output varies by machine calibration and operator technique — measure actual installed depth with a ruler at several points, not just trust the settings.
- ✕Skipping the settling allowance. Cellulose in particular compresses over the following months — buying the bare minimum bag count for your desired depth leaves you under target within a year.
- ✕Comparing DIY cost to a "full-service" pro quote without matching scope. Pro quotes often include air sealing, baffle installation, and cleanup that a straight bag-cost comparison doesn't capture.
Why trust this guide
Coverage rates and R-per-inch figures reflect standard manufacturer coverage charts for blown cellulose and fiberglass insulation. Installed cost ranges reflect 2026 US pricing data for professional attic insulation. Always confirm your specific product's exact coverage on the bag label, and get 2–3 local quotes if comparing against professional installation.
Frequently Asked Questions
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