Walls and layers
Start here when you need to compare masonry, insulation, cavities, and surface resistances in one model.
OpenBuilding Physics
Tool for quick thermal analysis of assemblies
Lambda Calculator
Choose a material, enter layer thickness, and calculate thermal properties for the full assembly.
Scope
Walls, roofs, floors, slabs
One place to select material, thickness, and verify U-value.
Start here
How to use LambdaCalculator
LambdaCalculator is a practical starting point for estimating thermal resistance R, U-value, and the effect of insulation thickness. It is built for homeowners, contractors, designers, and anyone comparing assembly options before discussing a project with a local professional.
Most common workflows
Floors and slabs
Check the resistance of existing layers, then compare several added insulation thicknesses.
OpenMaterials and lambda
Verify lambda values, R per inch, and common material data before entering assumptions in a calculator.
OpenPopular calculators
A short route to the tools most people need before choosing assembly layers.
Insulation thickness calculator
Compare the thickness needed for a U-value or R-value target before choosing a product.
OpenWhat the calculators handle
The tools connect R = d / lambda, U = 1 / total R, and conversions between R-value, U-factor, and SI units. Each result should be read together with the thickness, unit system, and material data source used to produce it.
The results are most useful for comparing options, preparing questions for a contractor, and deciding whether a thicker insulation layer deserves a closer look. They do not replace construction design, local code checks, or current manufacturer data sheets.
If you are unsure where to begin, choose the building element, enter the existing layers, compare two or three insulation options, and record the assumptions with the date and lambda source.
Units, languages, and limits
Metric and imperial
The site supports W/mK, W/m²K, m²K/W, R-value, U-factor, and thicknesses in mm, cm, and inches where the workflow needs them.
Languages
Public content is maintained in English, Deutsch, Español, Français, and Polski without a separate /en/ path.
Educational scope
Calculations are estimates and should be checked against local code, thermal bridges, and current manufacturer data.
Check the assumptions
These pages explain the formulas, terminology, and data maintenance approach before a result is used in a real project.
Assembly Builder
Add layers, choose materials, and update results live.
Surface Resistance
Results
Summary metrics and a layer table ready for print or export.
| Layer | Category | Material | Thickness | Lambda | R |
|---|
Formulas
R = d / lambda
U = 1 / (Rsi + sum(R layers) + Rse)
Notes
Thickness is entered in millimeters and converted to meters internally.
Material lambda values are indicative and should be verified in technical data sheets.
Lambda Calculator
Lambda Calculator
Lambda Calculator brings together calculators for building assemblies, materials, roofs, floors, concrete, electrical checks, and plumbing checks. The homepage keeps the layered thermal model visible while linking to focused tools for specific workflows.
The most reliable use is to compare options quickly, record assumptions, and then verify the result against current product data sheets. Testing more than one thickness is especially useful when a result is close to a local requirement.
All calculators and guides
A compact directory of published calculators, material pages, comparisons, and references in this language.
Frequently Asked Questions
Lambda is the thermal conductivity of a material, usually shown in W/mK. Lower lambda means heat moves through that material more slowly, but the final assembly still depends on thickness, surface resistances, and every other layer.
U-value describes heat loss through the whole building element, not just one material. A low U-value usually means a better insulated wall, roof, or floor, provided the real build-up matches the layers entered in the calculator.
Yes. Use the comparison section to keep thickness constant, then compare materials by lambda and calculated thermal resistance. This is useful when two products look similar on paper but behave differently at the same installed depth.
Yes. You can print the result or export it to CSV, Excel, or PDF for reports and documentation.
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 Lambda Calculator as a first-pass reference. Before specifying anything, compare the result with the project note, actual project dimensions, product data sheet, and local requirements.