Thermal Resistance & U-value Calculator

Build a layered assembly, inspect the resistance of every layer, and optionally add the surface-film values prescribed for your calculation method.

Add solid material layers from inside to outside. You can optionally add surface-film resistance values from your project method or standard; no default film values are assumed.

Construction layers

Layer 1
Layer 2
Layer 3

Optional surface-film resistance

Enter Rsi and Rse only when their values are defined by your applicable construction and calculation method.

Total thermal resistance (R)3.458 m²·K/W19.63 h·ft²·°F/Btu
Layer-only U-value0.289 W/(m²·K)0.051 Btu/(h·ft²·°F)
Surface-film resistance0 m²·K/WRsi 0 · Rse 0
U-value with supplied films0.289 W/(m²·K)Total R 3.458 m²·K/W
Layer resistance breakdown
Layerk [W/(m·K)]R [m²·K/W]
Layer 10.170.5882
Layer 20.0372.7027
Layer 30.60.1667

Important: conductivity varies with grade, moisture, density, temperature and installation. A code or energy-model U-value may also require surface films, repeating thermal bridges, air cavities, fasteners and junction losses.

Method

For each homogeneous layer, R = L / k. The total layer resistance is the sum of each layer's R-value, and U = 1 / Rtotal. If you supply inside and outside surface-film resistances, they are added separately and the calculator reports a second U-value.

Worked example

A 100 mm mineral-wool layer with k = 0.037 W/(m·K) has R = 0.100 / 0.037 = 2.70 m²·K/W. Its layer-only U-value is about 0.37 W/(m²·K). Add surface-film values only when your project method specifies them.

Important limits

This is not a whole-assembly or code-compliance calculation. The material presets are reference values, not product certification. Thermal bridges, framing, gaps, moisture effects, air movement, cavities, fasteners and junction details require their own treatment.

Related tools

Heat Loss Calculator · Heat Conduction Calculator · Heat Transfer Calculators

Frequently asked questions

How are thermal resistance and U-value calculated?
For each homogeneous layer, R = L / k. Layer resistances are added, and layer-only U-value is 1 divided by that total resistance.

Can I include inside and outside surface-film resistance?
Yes. Enter the Rsi and Rse values specified by your project method or standard. They are optional and default to zero, so the layer-only and supplied-film results remain distinct.

Can this calculator give a code-compliance U-value?
No. It is a transparent layer calculation. A code or energy-model assessment may also require thermal bridges, repeating framing, cavities, fasteners, junctions, moisture effects and the prescribed surface-resistance method.