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Insulation Thickness Calculator

Insulation thickness needed to reach a target U-value or R-value for a given material.

Also known as how thick insulation, insulation depth calculator, loft insulation thickness.

Enter values

Results update as you type.

Result

Insulation thickness

176.9 mm

Next standard thickness
200 mm
R-value needed from the insulation
5.0556 m²·K/W
Total R-value achieved
6.2143 m²·K/W
U-value achieved
0.1609 W/(m²·K)
Conductivity used
0.035 W/(m·K)

About the Insulation Thickness Calculator

Insulation thickness needed to reach a target U-value or R-value for a given material.

Also known as: how thick insulation, insulation depth calculator, loft insulation thickness, insulation needed for u value.

How to use this calculator

  1. Enter target, insulation, existing r-value of the structure and the other fields.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Insulation Thickness formula

thickness = (target R − existing R) × conductivity

Worked example

Using the values pre-filled in the calculator above:

  • Target: U-value
  • Target U-value = 0.18 W/(m²·K)
  • Insulation: Mineral wool (0.035)
  • Existing R-value of the structure = 0.5 m²·K/W

the calculator returns:

  • Insulation thickness: 176.9 mm
  • Next standard thickness: 200 mm
  • R-value needed from the insulation: 5.0556 m²·K/W
  • Total R-value achieved: 6.2143 m²·K/W