Layer resistance
For each uniform layer, thermal resistance is R = thickness in metres ÷ thermal conductivity λ.
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U-Value Calculator
Build up a simple wall, roof or floor layer by layer. Enter each material’s thickness and thermal conductivity (λ) to estimate total thermal resistance and U-value.
MaterialThickness (mm)λ (W/mK)R (m²K/W)
Estimated U-value
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Add one or more material layers to calculate.
Planning estimate only. Simple 1D layer calculations do not model repeating thermal bridges, fixings, non-uniform cavities or every requirement of a formal compliance calculation.
How the U-value calculation works
Total resistance
Add the resistance of every layer, plus the selected internal and external surface resistances.
U-value
For this simple construction model, U = 1 ÷ total thermal resistance. Lower U-values generally mean less heat flow.
Frequently asked questions
What is a U-value?
A U-value describes the rate of heat transfer through a building element. Lower values generally indicate better thermal performance.
What does λ mean?
Thermal conductivity, λ, is a material property measured in W/mK. A lower λ means the material conducts heat less readily.
Can I use manufacturer λ-values?
Yes. For a useful estimate, use the declared or design thermal conductivity appropriate to the product and calculation method you are working with.
Is this suitable for Building Regulations sign-off?
Use it as a planning estimate. Formal calculations can require treatment of repeating thermal bridges, fixings, cavities and other effects not included in this simple layer model.
Built for quick, transparent estimates. See how our calculators work and check page-specific assumptions before relying on a result.