Wall Insulation Calculator — m, R-value, cost
How to use this calculator
Enter wall dimensions using one of three methods: single wall (length x height), room perimeter (width x length x height), or direct area in square meters. Choose the unit (m, cm, or mm) from the dropdown. Specify door and window openings to subtract from gross area. Choose insulation type (batt/roll, blown-in, spray foam, or rigid board), stud spacing, and wall cavity depth. Results update instantly.
Cost — enter price per batt/bag/kit/sheet to get total material cost. Select your currency (EUR, PLN, CZK, etc.).
Vapor barrier — optional PE vapour control layer calculation based on net wall area.
U-value guidance — EN ISO 6946 recommended U-values displayed as reference.
U = 1/Rtotal (includes surface resistances Rsi=0.13, Rse=0.04 m2K/W per EN ISO 6946)
Country examples: DE: U ≤ 0.24 | FR: U ≤ 0.28 | PL: U ≤ 0.20 | CZ: U ≤ 0.30 | SE: U ≤ 0.18
Saved Calculations
| Time | Method | Net m2 | Type | R-value | U-value | Qty | Ins | VB | Total |
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How to Calculate Wall Insulation (Metric)
This wall insulation calculator estimates the amount of insulation needed for residential and commercial wall cavities using metric dimensions. Enter wall dimensions in meters, centimeters, or millimeters, subtract door and window openings, and choose from four insulation types: mineral wool or fiberglass batts, blown-in cellulose or fiberglass, open-cell or closed-cell spray foam, and rigid foam board (XPS, EPS, Polyiso). The calculator accounts for stud spacing (400 or 600 mm on center) and wall cavity depth (89 mm, 140 mm, or 200 mm).
Thermal Resistance and U-value
R-value (m2K/W) measures thermal resistance per EN ISO 6946. U-value (W/m2K) = 1/Rtotal where Rtotal includes surface resistances (Rsi=0.13 and Rse=0.04 m2K/W). Typical wall R-values: 2.3 m2K/W for 89 mm mineral wool, 3.7 m2K/W for 140 mm, and 5.3 m2K/W for 200 mm. Spray foam provides the highest R-value per thickness: closed-cell at ~0.045 W/mK vs mineral wool at ~0.035 W/mK.
Formulas
Net wall area = gross wall area - (doors x 1.89 m2) - (windows x avg W x avg H). Insulation packages = ceil(net area x (1 + waste%) / coverage per package). R-value = thickness / thermal conductivity. U-value = 1 / (Rsi + Rinsulation + Rse).
FAQ
Do I need a vapour barrier? In cold climates, a PE vapour control layer on the warm side of insulation prevents interstitial condensation per EN 13788. Check local building regulations. Can I mix insulation types? Yes, rigid board (continuous insulation) is often added over batt-insulated walls to reduce thermal bridging per EN ISO 10211.
