Insulation Calculator
Calculate insulation thickness and quantity from the required thermal resistance R: mineral wool, EPS, and XPS with their respective thermal conductivity λ.
Wall, roof, or floor area in square meters
Thermal resistance — typical values for walls in temperate climate are 3.0–3.5
Thermal conductivity λ defines the required slab thickness
How many square meters one pack covers
Calculation formula
Thickness = R × λ × 1000; Volume = Area × Thickness ÷ 1000; Packs = Area ÷ Pack coverage
R is the required thermal resistance (m²·K/W), λ is the thermal conductivity of the material (W/m·K). Thickness is returned in millimeters. Pack count is rounded up.
About the insulation calculator
This calculator returns the minimum insulation thickness from the simple formula δ = R × λ. Plug in the target thermal resistance required by your local building code and choose the material — mineral wool, expanded polystyrene (EPS), or extruded polystyrene (XPS).
On top of thickness it estimates the total insulation volume and the number of packs to order. That is convenient for budgeting and logistics: mineral wool packs typically cover 5–8 m², while a standard XPS pack of eight 600×1200×50 mm boards covers 5.76 m².
All math runs locally in your browser — nothing is uploaded. Add a 5–10% buffer for cuts and overlaps, especially when insulating roofs or facades with many openings.
Calculator benefits
Code-based math
We compute thickness from the material λ and the target R for your region
Pack count included
We show the number of packs to buy, rounded up by area
Any insulation type
Supports mineral wool, EPS expanded polystyrene, and XPS extruded polystyrene
FAQ
Where will the dew point be and how do I push it outside?
The dew point is the location inside the wall where water vapor in warm indoor air condenses into liquid water. With a properly sized exterior insulation layer the dew point shifts into the insulation or further outside, so the load-bearing wall stays dry. If the insulation is too thin or installed on the inside, the dew point ends up at the wall–insulation interface and the wall starts to soak and grow mold.
What R-value do building codes require for walls and roofs?
Most national codes prescribe a target thermal resistance based on the climate zone. As a rough guide for a temperate climate: walls 3.0–3.5 m²·K/W, floors above unheated basements 4.0–4.6, pitched roofs and ceilings under cold attics 4.5–5.5. Warmer regions allow lower values, while subarctic zones require higher ones. Check your local energy code for the exact figure.
Mineral wool or polystyrene foam — which one to choose?
Mineral wool is vapor-open, non-combustible, and a good fit for timber and steel-framed walls, ventilated rainscreens, and roofs. EPS and XPS are cheaper and do not absorb water, but they block vapor — they fit best on plinths, foundations, and ground-floor slabs, and on walls only with a proper interior vapor barrier. For breathable wall assemblies mineral wool is the safer default.
Why does vapor permeability matter?
Vapor permeability tells you how easily water vapor passes through a material. Rule of thumb: layers in a wall should go from less permeable on the inside to more permeable on the outside. Putting XPS on the outside of an autoclaved aerated concrete wall traps vapor and the wall starts to wet — you would need a strict interior vapor barrier or a switch to mineral wool.