What does lambda mean in building materials?

Lambda is the thermal conductivity of a material, usually expressed in W/mK. Lower lambda values indicate better insulation performance.

How is U-value calculated?

U-value is calculated as 1 divided by the total thermal resistance of the assembly, including surface resistances and all layer resistances.

Can I compare insulation materials by thickness?

Yes. The calculator includes a comparison area where you can choose materials, set thickness, and compare lambda and calculated thermal resistance.

Can I print or export the result?

Yes. You can print the result or export it to CSV, Excel, or PDF for reporting and documentation.

Does the calculator work for walls, roofs, and floors?

Yes. It is designed for layered assemblies such as external walls, flat roofs, pitched roofs, floors, and slabs.

Is the calculator suitable for quick design checks?

Yes. It is intended for fast concept-stage calculations, insulation comparison, and envelope optimisation before detailed design.

Can I switch thickness units?

Yes. You can switch between millimeters, centimeters, and inches, and the calculator keeps the values consistent.

Building Physics

A fast thermal analysis tool for building assemblies

Lambda Calculator

Choose a material, enter the layer thickness, and calculate the thermal parameters of the full assembly. The tool runs without installation and can be published directly as a website.

Calculate

Layer calculations PDF / Excel export Online publishing

Zakres Sciany, dachy, podlogi, stropy

Jedno miejsce do doboru materialu, grubosci i sprawdzenia U.

Assembly Builder

Add layers, choose materials, and update results live.

Surface Resistances

Thickness unit Internal Rsi (m2K/W) External Rse (m2K/W) Assembly name

Results

Summary and layer table for print or export.

Total resistance 0.00 m2K/W

U-value 0.00 W/m2K

Average lambda 0.00 W/mK

Total thickness 0 mm

Layer	Category	Material	Thickness	Lambda	R

Formulas

R = d / lambda

U = 1 / (Rsi + sum(R layers) + Rse)

Notes

Enter thickness in millimeters and the calculator converts it to meters.

Lambda values in the database are approximate. For detailed design, confirm them in the manufacturer data sheets.