Insulation · Project planning

Insulation R-Value Calculator

Convert US R, SI RSI or an entered U-value, sum layers, or compare frame and cavity heat-flow paths. U-values are reported with their unit system explicitly identified.

By Alish Gautam, Software Developer · Updated · Calculation methodology

Start with the editable example below. Dimensions retain their physical size when units change. Region sets currency labels without converting currencies; confirm entered quotes after changing region. Thermal inputs labeled US R retain that unit in every region.

Basic settings
Choose the estimating method.
All entries use the selected R or RSI mode. Do not mix numerical unit systems.

Project takeoff

Whole packages round up. Allowance is separate from purchased surplus. Prices omit labor, delivery, tax and other items unless explicitly entered.

US R-value
14.5 ft²·°F·h/Btu
SI RSI
2.554 m²·K/W
SI U-value
0.392 W/(m²·K)
US U-factor
0.069 Btu/(h·ft²·°F)

Enter complete path resistances including any intended films. The simple parallel model does not certify a complex wall, two-dimensional bridge or condensation behavior.

How it works

RSI = US R × 0.1761101838. Series resistance adds; U = 1 / resistance in matching units. Entered SI U gives RSI = 1 / U; entered US U gives R = 1 / U. Parallel U = frame fraction / frame-path R + cavity fraction / cavity-path R.

Assumptions and limitations

Enter complete path resistances including any intended films. The simple parallel model does not certify a complex wall, two-dimensional bridge or condensation behavior.

Whole packages round upward after the chosen allowance. Physical geometry and purchase reserve are separate. Manufacturer and project specifications override editable examples; the selected region does not establish a local code requirement.

Sources and boundaries

Natural Resources Canada: Keeping the Heat In — Section 3: Materials

Open the source · Web guidance; edition not stated · Reference checked 2026-10-04

Scope: Material and thermal-control guidance

Used for: R versus RSI terminology; Assembly-specific material considerations.

Does not establish: All products share one R per inch; Provincial code lookup.

Thermal conversion is a unit conversion; product resistance is an input.

ENERGY STAR: Recommended Home Insulation R-Values

Open the source · Web guidance; edition not stated · Reference checked 2026-10-04

Scope: US residential retrofit recommendations

Used for: Displayed climate-zone attic reference table.

Does not establish: Local adopted-code compliance; Manufacturer bag coverage.

The page states its guidance is based on 2021 IECC Table R402.1.3; preserve separate bare-attic and existing-insulation columns.

Australian Building Codes Board: NCC — Building Fabric

Open the source · NCC 2022 Housing Provisions, Part 13.2 · Reference checked 2026-10-04

Scope: Published housing building-fabric provisions

Used for: Assembly and climate-zone context.

Does not establish: Universal ceiling R value; Current state adoption determination.

Linked adopted 2022 text is an identified reference, not a claim that every project uses that edition. Confirm current jurisdiction adoption and project pathway.