Complete Guide: How Much Insulation Do You Need for Your R-Value Target?
An insulation calculator converts your target R-value and insulation type into the exact thickness you need to install. This free tool applies standard R-value-per-inch figures for common insulation materials, since different products need very different thicknesses to hit the same R-value.
💡 Quick Summary
Required thickness (inches) = target R-value ÷ R-value per inch of your chosen material. Spray foam achieves the highest R-value per inch, meaning it needs the least thickness for the same insulating performance.
Common Target R-Values by Location
- R-13 to R-19: Typical for standard exterior wall cavities (2x4 or 2x6 framing).
- R-30 to R-38: Common for attic floors in moderate to cold climates.
- R-49: Recommended for attic floors in very cold climates for maximum energy efficiency.
R-Value Per Inch by Insulation Type
| Insulation Type | R-Value per Inch |
|---|---|
| Blown-In Fiberglass | ~2.5 |
| Fiberglass Batt | ~3.2 |
| Blown-In Cellulose | ~3.5 |
| Closed-Cell Spray Foam | ~6.5 |
Step-by-Step Instructions
- Enter the area you're insulating in square feet.
- Select your target R-value.
- Select your insulation type.
- Click ⚡ Calculate Insulation Needed.
- Review your required thickness and total volume, then use 📋 Copy Summary to save your results.