U-WertRechner.com provides free online tools and guidance to help homeowners and building professionals assess the thermal performance of building components. Its calculator estimates U-values in accordance with DIN EN ISO 6946, using the selected materials, layer thicknesses and thermal conductivity values. Users can model wall, roof and other constructions, add layers, review insulation performance and check results against German GEG requirements. A PDF export is available, along with an Excel-based calculator for offline use.

The site also offers specialized calculators for exterior walls, roofs, floor slabs, windows, wooden window frames and glazing, including calculations for overall window U-values and glass Ug-values. Supporting resources explain U-values, lambda and thermal resistance, summarize GEG and KfW benchmarks, and outline insulation materials and example manufacturers. Practical articles address common planning concerns such as thermal bridges, moisture protection, condensation and renovation preparation. The service describes its calculations as guidance rather than documentation for building-permit applications, which require a qualified professional.