About the Cellulose Insulation Calculator
Settling Factor: Cellulose in open-blow attic applications settles 15-20% over the first 1-2 years. Professional installers typically blow to a depth 15-20% greater than the minimum to compensate. The depth shown is the minimum required — consider adding 15-20%.
⚠️ Vapor Barrier: In cold climates (Zones 5-8), wall cavity insulation requires a Class I or II vapor retarder on the warm side per IRC R702.7. Dense-packing walls without proper moisture management can cause mold and structural rot.
Dense-Pack Note: Dense-pack cellulose installation requires professional equipment capable of achieving 3.5 lb/cu ft density. Standard attic blowing machines cannot achieve this density. Under-dense installation will settle and create gaps at the top of wall cavities.
Cellulose insulation is one of the most cost-effective and environmentally friendly insulation options available. Made primarily from recycled newspaper treated with fire retardants, it provides an R-value of approximately 3.5 per inch when blown in at the proper density. This calculator helps you determine exactly how many bags you need based on your area, target R-value, and any existing insulation.
The R-value you need depends on your climate zone and the area being insulated. Walls typically require R-13 to R-15, while attic insulation in moderate climates should be R-30 to R-38. In cold northern climates, R-49 or higher is recommended for attic spaces. If you have existing insulation, this calculator accounts for its contribution so you only add what is needed to reach your target.
A standard 25-pound bag of cellulose yields approximately 25 cubic feet when blown into open attic spaces at the standard density of about 1.5 lb/cu ft. However, for wall dense-pack applications, the required density is approximately 3.5 lb/cu ft to prevent settling, which means each 25-lb bag only yields about 7 cubic feet. This applies to any wall cavity application, including common R-19 dense-pack in 2x6 walls and R-13 in 2x4 walls. Use the Application Type selector to choose between attic open-blow and wall cavity dense-pack, and the calculator will apply the correct bag yield. If you have existing insulation of a different type, select the material so the calculator correctly converts its R-value contribution before determining how much cellulose to add. A 10% waste factor is included in all estimates.