What this site is
Loft Insulation Calc is a free calculator for homeowners who want to know how much insulation they need, what to buy and roughly what it will cost, before they talk to a store or a contractor.
You tell it what you're insulating, how big it is, what's there now and where you live. It works out the R-value to add, the depth, the number of bags or sheets and a material cost range, and it shows every step of the math.
How it's built
- Free, with no sign-up. There are no accounts and nothing to unlock.
- Runs in your browser. The calculation happens on your device. Your inputs are kept only in the page address, so you can bookmark or share a result.
- No cookies. We don't use cookies or cross-site tracking. See our privacy policy for the details.
- Sourced. Targets come from ENERGY STAR and the 2021 IECC, quantities from manufacturers' coverage charts and product sheets, and prices from typical retail listings. Every page lists its sources, and the methodology explains each formula.
Where it works
The site has separate sections for four countries, each with its own rules, products and units:
- United States: R-values by IECC climate zone, found from your ZIP code
- United Kingdom: U-values from the Building Regulations
- Germany: U-values for the GEG and federal funding rules
- France: thermal resistance targets for renovation programs
Independence and how the site is funded
Loft Insulation Calc isn't owned by, or paid by, any manufacturer or retailer. Brand names appear only because their published data sheets and coverage charts are the sources for our numbers.
The site is free to use. In the future it may carry advertising or affiliate links to help cover its costs. If it does, those links won't change the calculations, and we'll say so clearly. Read our affiliate disclosure for how that would work.
Contact
Found an error, or have a suggestion? Email info@loftinsulationcalc.com. Corrections to data or formulas are especially welcome.
Our terms of use explain what the estimates are and aren't.