Insulation R-Value & U-Value Calculator
Build your wall, roof or floor one layer at a time and get its real U-value — with the surface films, air gaps and the timber or steel bridging that most calculators quietly leave out.
What are you building?
This sets the surface resistances — heat leaves a roof differently than a wall
Advanced / Custom Input — surfaces
Filled in from the assembly type.
m²K/W
m²K/W
Anything the layer list does not cover.
m²K/W
The layers
Add them in order, from the inside face out. Pick a material and the conductivity fills itself in — change it if you have the figure from the product datasheet.
Advanced / Custom Input — the layers
Replaces the layer list with a worked starting point.
Studs and joists
Studs and joists carry heat straight past the insulation
%
Advanced / Custom Input — bridging
Softwood is about 0.13. Steel is about 50, which is why steel framing hurts so much.
W/mK
Used with the spacing to work out the percentage.
mm
What are you aiming for?
Filled in from your country. Lower is better.
W/m²K
Used for the condensation caution only
°C
Advanced / Custom Input — the target
Filled in from your country. Used for the condensation caution.
°C
%
Result
Add your layers, then press “Work out the U-value”.
Calculated to ISO 6946. Estimate only — verify with a qualified engineer and your local building control before relying on it.
1
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mm
W/mK