Insulation Calculator
How to Use the Insulation Calculator Select the area type (attic, walls, floor, or basement), enter dimensions, add the number of doors and windows to deduct, choose your insulation type, and select your target R-value. Click Calculate for the total area, required thickness, number of bags or rolls, and estimated material cost. R-Value Explained R-value […]
How to Use the Insulation Calculator
Select the area type (attic, walls, floor, or basement), enter dimensions, add the number of doors and windows to deduct, choose your insulation type, and select your target R-value. Click Calculate for the total area, required thickness, number of bags or rolls, and estimated material cost.
Air sealing is as important as R-value. Before adding any insulation, seal all penetrations — electrical boxes, plumbing pipes, attic hatches, and recessed lights. Even a perfectly insulated attic loses most of its value through unsealed gaps.
R-Value Explained
R-value measures thermal resistance — how effectively a material resists heat flow. A higher R-value means better insulation. The value is additive: two layers of R-13 insulation give you R-26 total. All insulation products display their R-value per inch — multiply by the installed thickness to get the total R-value. The DOE recommends R-49 to R-60 for attics in most of the continental US. Walls typically target R-13 (2×4 framing) to R-20 (2×6 framing).
Insulation Types Compared
Fiberglass batts are the most widely installed insulation in the US — inexpensive, DIY-friendly, and available everywhere. The key is installation quality: gaps, compression, and voids dramatically reduce effective R-value. Mineral wool (Rockwool) batts are denser, naturally fire-resistant, and maintain R-value when wet — worth the premium in humid climates. Blown-in cellulose has good thermal performance and is made from recycled material, but can settle over time. Spray foam (closed-cell) has the highest R-value per inch at R-6.5, creates a complete air barrier, and is the best choice for tight spaces and difficult geometries — but requires professional installation and costs 3–5× more than batts.
FAQs
How much insulation do I need in my attic?
The DOE recommends R-38 to R-60 for attics depending on climate zone. For most of the US (Climate zones 4–5), R-49 is the target. Fiberglass blown-in insulation achieves R-49 at approximately 16–18 inches of depth. If your attic currently has R-19 (6 inches of old fiberglass), you need to add approximately 10 more inches of blown-in to reach R-49. Use the calculator above to get an exact figure for your attic dimensions.
Will adding insulation reduce my energy bills?
Yes — heating and cooling accounts for 40–50% of a typical home’s energy bill. The EPA estimates that properly air sealing and insulating can cut energy costs by 15% on average, with poorly insulated older homes seeing savings of 20–30%. Attic insulation has the fastest payback period — typically 2–4 years. The incremental gain from R-19 to R-38 is significant; from R-38 to R-60 is smaller. Proper air sealing often provides as much benefit as adding R-value.