US R-value tools
R-value calculator for insulation, U-factor, and U-value
This R-value calculator is the main US hub for insulation planning. Enter a thickness and a k-value, choose a material preset when you want a quick starting point, then read the result as R-value, RSI, U-factor, and European U-value. The page is written for product comparison, code pre-checks, renovation estimates, and cross-border datasheets where inch-based labels and metric lambda values appear together. R-value is a resistance number, so higher is better. U-factor and U-value are heat-transfer numbers, so lower is better. When you use imperial mode, thickness is handled in inches and conductivity is handled as k-value in Btu·in/(h·ft²·°F). When you switch to metric mode, the same interface uses millimetres and lambda in W/mK. The conversion path stays visible because most mistakes happen when someone inverts a US R-value and calls it a European U-value without applying the 5.678263337 unit factor.
Calculations keep US R-value, U-factor, SI R, and SI U-value separate so an inverted value is not mislabeled.
Quick answer
R-value calculator for insulation, U-factor, and U-value
For a single homogeneous layer, use R-US = thickness in inches / k-value. If the material label gives R per inch instead of k-value, multiply R per inch by installed thickness. For metric product sheets, first calculate RSI = thickness in metres / lambda, then multiply RSI by 5.678263337 to get US R-value. Once the R-value is known, U-factor is 1 / R-US and SI U-value is U-factor × 5.678263337. A 5.5 in cavity layer with k = 0.25 gives R-22, RSI 3.875, U-factor 0.045, and U-value 0.258 W/m²K before framing, gaps, compression, or air films are considered.
- Formula
R_US = thickness_in / k- Example
- Example: 7.25 in of insulation at k = 0.25 gives R-29.0, RSI 5.11, U-factor 0.034, and U-value 0.196 W/m²K before assembly corrections.
Working calculator
Enter the core dimensions and check the result directly on this page.
R-value conversion table
Common R-values shown with US U-factor and metric SI U-value.
| Input | US U-factor | SI U-value | Practical reading |
|---|---|---|---|
| R-13 | 0.077 | 0.437 W/m²K | common cavity insulation |
| R-19 | 0.053 | 0.299 W/m²K | typical wall check |
| R-30 | 0.033 | 0.189 W/m²K | stronger layer |
| R-49 | 0.020 | 0.116 W/m²K | high resistance |
Worked examples
Example 1
Inputs
d = 5.5 ink = 0.25
Formula
R_US = thickness_in / k
Steps
5.5 / 0.25 = 22
Result
R_US = R-22
Related calculator
R-value calculatorExample 2
Inputs
R_1 = R-13R_2 = R-5
Formula
R_total = R_1 + R_2
Steps
13 + 5 = 18
Result
R_total = R-18 before framing effects
Related calculator
Wall R-valueR-value calculator for insulation, U-factor, and U-value
Example: 7.25 in of insulation at k = 0.25 gives R-29.0, RSI 5.11, U-factor 0.034, and U-value 0.196 W/m²K before assembly corrections.
Zero and negative values are not meaningful for these conversions. The calculator clamps inputs above zero and the text explains which unit system each value belongs to.
Practical note
Before you use the result
R-value calculator for insulation, U-factor, and U-value is intended for quick option checks and technical discussion before detailed execution. The result depends on the selected units, declared material values, and chosen surface resistances, so each change in layer or thickness should be treated as a separate variant.
The calculator does not automatically verify every local rule, thermal bridge, moisture condition, structural connection, or installation tolerance. If the result is close to a requirement, treat it as a reason for deeper verification rather than a final decision.
For better comparisons, test several realistic thicknesses, check current product data sheets, and review the complete assembly. A calculated value is most useful when the assumptions are clear: material, thickness, layer order, units, and data source.
For insulation or U-value tools, layer order and correct units are especially important. For concrete, electrical, plumbing, or heating tools, the result should be read as a quick quantity or plausibility check before standards and execution conditions are reviewed.
Save the result with the date, material name, and assumptions. If the product, diameter, cable section, or thickness changes later, do not compare the numbers alone without checking which inputs changed.
For calculator pages, clear separation between inputs and result is essential. If a value looks surprising, check units and default fields first, then review the project assumptions.
R-value Calculator
R-value Calculator
Calculate US R-value from thickness and k-value, compare R per inch, and convert the result to RSI, U-factor, and SI U-value.
Assembly thickness
Assembly thickness
Use thickness in inches with k-value, or switch to metric mode for millimetres and lambda. The calculator labels each unit before showing the result.
U-value
U-value
R-value and U-factor move in opposite directions: higher R-value is better, while lower U-factor or lower U-value is better.
CategoryLambdaLayerMaterialThickness
How it works
Unit assumptions
R-value from thickness and conductivity is only a layer calculation. It does not automatically include studs, fasteners, air films, cavities, rain screens, or installation quality. Add layers when heat flows through the same path; use a parallel-path or area-weighted method when framing bypasses insulation.
How to use the result
The hub links to direct converters for R-value to U-factor, U-factor to R-value, R-value to SI U-value, SI U-value to US R-value, lambda to R-value, and thickness in inches. Use those pages when a datasheet already gives the value you need to convert.
R-value Calculator
For a single homogeneous layer, use R-US = thickness in inches / k-value. If the material label gives R per inch instead of k-value, multiply R per inch by installed thickness. For metric product sheets, first calculate RSI = thickness in metres / lambda, then multiply RSI by 5.678263337 to get US R-value. Once the R-value is known, U-factor is 1 / R-US and SI U-value is U-factor × 5.678263337. A 5.5 in cavity layer with k = 0.25 gives R-22, RSI 3.875, U-factor 0.045, and U-value 0.258 W/m²K before framing, gaps, compression, or air films are considered.
Use the material preset as an estimating aid, not as a substitute for the manufacturer’s declared value. Fiberglass, mineral wool, EPS, XPS, and polyiso can overlap by density, facing, blowing agent, temperature, and aging method. The same R-value can also behave differently in a real wall because framing fractions, metal penetrations, air leakage, and compression reduce whole-assembly performance. For a quick product check, compare R per inch. For a code or energy-model check, convert the total installed R-value into U-factor and verify that the whole assembly still meets the target after thermal bridges and surface films are included.
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Assembly nameThickness unitInternal Rsi (m2K/W)External Rse (m2K/W)
Calculation assumptions
The calculators use visible formulas and explicit unit conversions. Treat the result as a preliminary check, not a complete building design.
- SI and US units are converted separately; R, RSI, U-value, and U-factor are not mixed without the unit factor.
- Enter positive values and compare the result with the selected product datasheet.
- Local codes, thermal bridges, fasteners, and installation quality can change the requirement.
- Last formula review: 2026-04-27.
See how formulas, unit conversions, rounding, and limitations are handled. Methodology details.
US R-value mini-hub
Move between R-value calculators, material tables, insulation comparisons, and assembly calculators without scanning the whole navigation.
R-value calculators
Material R-values
Insulation comparisons
Assembly calculators
Reference tables
Using European units?
Open the U-value, lambda, and metric insulation thickness tools.
Materials and comparisons
Check lambda values, insulation comparisons, and reference pages before choosing layers.
R-value conversion FAQ
No. Zero resistance or zero transmittance would make the inverse formula impossible or physically meaningless.
They describe heat transfer in different unit systems. US U-factor uses Btu/(h·ft²·°F), while SI U-value uses W/m²K.
Higher is better for R-value because it is resistance. Lower is better for U-factor and U-value because they measure heat transfer.
Use them for checks and comparisons, then confirm manufacturer declarations, assembly corrections, and local code rules.
Yes. It is designed for layered assemblies such as external walls, flat roofs, pitched roofs, floors, and slabs. For unusual assemblies, add every relevant layer and treat the result as a planning check before formal verification.
Yes. It is intended for fast concept-stage calculations, insulation comparison, and envelope optimisation before detailed design. It is best used to narrow choices, not to replace a code check or project-specific thermal bridge assessment.
Yes. You can switch between millimeters, centimeters, and inches, and the calculator keeps the values consistent. For fewer mistakes, choose one unit system at the start of a project and review converted thicknesses before export.
Use R-value calculator for insulation, U-factor, and U-value as a first-pass reference. Before specifying anything, compare the result with the installation tolerance, actual project dimensions, product data sheet, and local requirements.