Insulation Calculator
Batts or rolls needed by R-value.
Enter your values
Enter the area to insulate in sq ft.
Enter the coverage per bag/roll in sq ft.
Enter the price per bag/roll in $.
Choose one of: R-13 walls, R-19, R-30, R-38 attic, R-49 attic.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Bags or rolls needed
- 20
- Area with 5% waste
- 945 sq ft
- Target R-value
- R-38
- Estimated cost
- $840.00
- Cost per square foot
- $0.93
Quick answer
Insulation is sized by area and R-value; higher R means more thickness and better heat resistance.
At a glance
| What it does | Batts or rolls needed by R-value. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Area to insulate, Coverage per bag/roll, Price per bag/roll, Target R-value |
| Main output | Bags or rolls needed |
| Cost | Free — no sign-up, no download |
How to use the Insulation Calculator
- 1Measure the area to be insulated.
- 2Check coverage per bag on the label.
- 3Pick the R-value recommended for your climate zone.
Inputs explained
- Area to insulate(sq ft)
- Enter the area to insulate in sq ft.
- Coverage per bag/roll(sq ft)
- Enter the coverage per bag/roll in sq ft.
- Price per bag/roll($)
- Enter the price per bag/roll in $.
- Target R-value
- Choose one of: R-13 walls, R-19, R-30, R-38 attic, R-49 attic.
Worked example
Using the values the calculator loads with:
Inputs
- Area to insulate900 sq ft
- Coverage per bag/roll48 sq ft
- Price per bag/roll42 $
- Target R-valueR-38 attic
Results
- Bags or rolls needed20
- Area with 5% waste945 sq ft
- Target R-valueR-38
- Estimated cost$840.00
- Cost per square foot$0.93
Frequently asked questions
What R-value do attics need?
R-38 to R-60 depending on climate zone.
Can I add over old insulation?
Yes, as long as the new layer is unfaced.
What do I need to enter into the Insulation Calculator?
Just 4 values: area to insulate, coverage per bag/roll, price per bag/roll, target r-value. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Insulation Calculator work out the answer?
Insulation is sized by area and R-value; higher R means more thickness and better heat resistance. The working is shown step by step so you can verify the result by hand.
Is the Insulation Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.