Insulation Calculator — How Much Insulation Do I Need?
Enter your area, insulation type, and target R-value to get the bags or packages needed.
How to Calculate Insulation Needed
Insulation coverage isn't just about square footage — it's about square footage at a specific thickness (R-value). The same bag of blown-in insulation covers far more area at R-30 than it does at R-49, because higher R-values require a thicker, denser layer.
Calculate your area (length × width), choose your insulation type and target R-value for your climate zone, and the coverage-per-bag figure for that specific combination determines how many bags or packages you need.
Recommended R-Values by Area
| Area | Recommended R-Value |
|---|---|
| Attic (most US climates) | R-38 to R-60 |
| Exterior walls | R-13 to R-21 |
| Floors over unheated space | R-25 to R-30 |
| Basement walls | R-10 to R-19 |
Colder northern climate zones need the higher end of each range; warmer southern climates can typically use the lower end. Check your local energy code for the exact requirement in your area.
Frequently Asked Questions
What R-value do I need for my attic?
Most US climate zones recommend R-38 to R-60 for attic insulation. Colder northern climates need the higher end; warmer southern climates can use R-30 to R-38.
How many bags of blown-in insulation do I need for an attic?
Coverage per bag depends on your target R-value and insulation type — a bag of blown-in fiberglass covers roughly 32 sq ft at R-30, but only about 20 sq ft at R-49, since more material is needed per square foot at higher R-values.
Is blown-in or batt insulation better for an attic?
Blown-in insulation fills gaps and irregular spaces around joists and wiring more completely, making it the more common choice for attics. Batt insulation is easier to install without special equipment and works well for open, regularly-shaped wall cavities.
Do I need to remove old insulation before adding new insulation?
Not usually. New insulation can typically be added directly on top of existing insulation, as long as the old material is dry and not damaged by mold or pests.