An attic insulation calculator determines exactly how many bags of blown-in insulation you need to reach your target R-value. By factoring in your attic square footage, climate zone, current insulation level, and material type, this tool calculates the required depth, number of bags, estimated cost, and potential energy savings from the upgrade.
Attic Details
Climate Zone & Insulation Type
Auto-filled from climate zone (adjustable)
Calculation Details
Insulation Type Comparison
All three types calculated for your attic to reach R-49
| Property | Fiberglass | Cellulose | Mineral Wool |
|---|
Estimated Energy Savings
Adding insulation can reduce heating and cooling costs significantly.
Bag counts include 5% overage for waste. Cost estimates are for materials only — professional installation typically adds $1.00-1.50 per square foot. Actual energy savings depend on climate, home sealing, and HVAC efficiency.
How to Use the Attic Insulation Calculator
Adding blown-in attic insulation is one of the most cost-effective home energy upgrades, often paying for itself in reduced heating and cooling bills within 2-3 years. This calculator helps you determine exactly how many bags of insulation you need, how deep to blow it, and how much it will cost.
Step 1: Enter Your Attic Dimensions
Start by entering your attic square footage. If you do not know the exact number, measure the length and width of your house footprint — most attics cover roughly the same area as the floor below. Then select your current insulation level. If your attic has old batts or some blown-in insulation, select the closest R-value. Choose "None" for an uninsulated attic.
Step 2: Select Your Climate Zone
Your climate zone determines the recommended R-value for your attic. Warmer southern states (Zones 1-3) need R-30 to R-49, while colder northern states (Zones 5-7) need R-49 to R-60. The calculator auto-fills a recommended target R-value, but you can adjust it up or down based on your preference and budget.
Step 3: Choose Your Insulation Type
Select from fiberglass, cellulose, or mineral wool blown-in insulation. Cellulose is the most popular for DIY projects due to its lower cost and higher R-value per inch. Fiberglass is lighter and does not absorb moisture. Mineral wool has the best fire resistance but costs more per bag. The comparison table shows all three options side by side.
Step 4: Review Your Results
Click "Calculate Insulation Needs" to see the additional R-value needed, required depth in inches, number of bags (including 5% overage for waste), and estimated material cost. The comparison table lets you quickly see how the three insulation types differ in depth, bags, cost, and characteristics for your specific attic.
Tips for a Successful Insulation Project
Before blowing in insulation, seal all air leaks around light fixtures, plumbing penetrations, and the attic hatch. Air sealing alone can save 10-20% on energy bills. Install baffles at eaves to maintain soffit ventilation. Keep insulation away from recessed lights unless they are rated IC (insulation contact). Many home improvement stores offer free blower machine rentals with a minimum bag purchase.
FAQ
Is this attic insulation calculator really free?
Yes, completely free with no signup required. All calculations run locally in your browser — no data is sent to any server. Use it as many times as you need to compare different insulation types and coverage levels.
Is my data safe when using this tool?
Absolutely. Everything runs entirely in your browser using JavaScript. No attic dimensions, addresses, or personal information is transmitted anywhere. You can even use it offline once the page loads.
How do I know what R-value I need for my attic?
The required R-value depends on your climate zone. Zones 1-3 (warmer southern states) need R-30 to R-49. Zones 4-5 (mid-latitude states) need R-38 to R-60. Zones 6-7 (cold northern states) need R-49 to R-60. This calculator auto-fills the recommended target based on your zone.
What is the difference between fiberglass and cellulose blown-in insulation?
Fiberglass is lightweight, non-combustible, and resists moisture but has lower R-value per inch (about R-2.5). Cellulose is made from recycled paper, has a higher R-value per inch (about R-3.7), is cheaper per bag, and fills gaps better. However, cellulose is heavier and can settle over time.
How many bags of insulation do I need for a 1,000 square foot attic?
It depends on the insulation type and target R-value. For cellulose blown to R-30, you need about 31-32 bags. For fiberglass blown to R-30, you need about 40 bags. For R-49, you will need roughly 50 bags of cellulose or 63 bags of fiberglass. This calculator gives you exact numbers based on your inputs.
Can I add blown-in insulation on top of existing insulation?
Yes, adding blown-in insulation over existing batts or blown-in is a common and effective approach. Just select your current R-value in the calculator, and it will determine how much additional insulation you need to reach your target. Make sure existing insulation is dry and not compressed before adding more.
How much does blown-in attic insulation cost?
Material costs range from $1.00 to $2.50 per bag depending on the type. Fiberglass averages $1.50 per bag, cellulose about $1.25, and mineral wool about $2.00. For a typical 1,000 sq ft attic to R-49, expect $50-130 in material costs. Professional installation typically adds $1.00-1.50 per square foot.