Insulation R-Value Calculator

Understanding Insulation R-Values

Not sure how much insulation you actually have once layers get stacked together? This calculator makes it easy to total the R-value of a wall, roof, or floor assembly so you can compare options and make smarter energy-efficiency decisions. It is designed for homeowners, DIYers, and builders who want a quick, reliable way to estimate thermal resistance without digging through tables or complicated formulas.

What R-value means (in plain language)

R-value describes how well a material resists heat flow. Higher numbers mean better insulation. Think of it as a blanket for your home: a thicker, denser blanket keeps warmth in during winter and slows heat gain in summer. When you layer materials, their R-values add together. That total represents the overall insulation performance of your assembly.

Why the “system” matters

Real walls and roofs are made of more than insulation. Framing, drywall, sheathing, and air gaps can raise or lower the effective R-value. For example, wood studs act as thermal bridges with much lower R-values than the insulation between them. This calculator helps you account for multiple layers so you can see the full picture instead of relying on a single label like “R-13.”

How to use the calculator

Start by listing each layer in your assembly. Common layers include drywall, fiberglass batts, mineral wool, spray foam, rigid foam board, and exterior sheathing. Choose the material and enter its thickness. If you have a custom material, you can input the R-value directly. Click “Add Layer” for each layer you want to include, then hit “Calculate Total R-Value.” The result shows the total R-value and the equivalent U-value (the rate of heat transfer).

Real-world examples

Use this tool to compare attic insulation upgrades, confirm if a basement wall meets local energy code requirements, or plan a remodel that adds continuous exterior insulation to reduce thermal bridging. It is also helpful when comparing different insulation types, such as closed-cell spray foam versus fiberglass batts, or when evaluating how much rigid foam you need for a garage or workshop.

Tips for better results

Insulation performance depends on proper installation, air sealing, and moisture control. Gaps, compression, and air leaks reduce the effective R-value. For the most accurate estimate, use the actual thicknesses and materials you plan to install, and remember that the assembly’s total insulation level is what drives comfort and heating or cooling costs.