Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Fiberglass 3.2, cellulose 3.6, closed-cell foam 6.5
Result
Packages needed
15
Required depth (in)
11.9
Material cost
$870
Cost per sq ft
$0.73
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter area to insulate (sq ft).
- 2Enter target r-value.
- 3Enter r-value per inch — Fiberglass 3.2, cellulose 3.6, closed-cell foam 6.5.
- 4Enter coverage per package (sq ft).
- 5Enter price per package ($).
- 6Read your packages needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
R-value is resistance to heat flow per inch of material. Compressing a batt into a shallower cavity reduces its R-value, so match the batt thickness to the framing depth.
Worked example
Using the values the calculator loads with:
Inputs
- Area to insulate: 1200 sq ft
- Target R-value: 38
- R-value per inch: 3.2
- Coverage per package: 88 sq ft
- Price per package: 58 $
Results
- Packages needed: 15
- Required depth (in): 11.9
- Material cost: $870.00
- Cost per sq ft: $0.73
What each field means
Inputs
- Area to insulate (sq ft)
- The area to insulate used in the calculation, measured in sq ft. Starts at 1200 sq ft so you have a working example on load.
- Target R-value
- The target r-value used in the calculation. Starts at 38 so you have a working example on load. Accepted range: 5–80.
- R-value per inch
- Fiberglass 3.2, cellulose 3.6, closed-cell foam 6.5
- Coverage per package (sq ft)
- The coverage per package used in the calculation, measured in sq ft. Starts at 88 sq ft so you have a working example on load.
- Price per package ($)
- The price per package used in the calculation, measured in $. Starts at 58 $ so you have a working example on load.
Results
- Packages needed
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Required depth (in)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Material cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cost per sq ft
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the insulation calculator work?
R-value is resistance to heat flow per inch of material. Compressing a batt into a shallower cavity reduces its R-value, so match the batt thickness to the framing depth. The underlying maths is: Bags or batts = Area ÷ Coverage per package, plus waste. Depth = Target R ÷ R per inch.
What do I need to enter?
5 values: area to insulate, target r-value, r-value per inch, coverage per package, and price per package. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the packages needed result mean?
It is returned as a whole number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Insulation Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/insulation
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/insulation" target="_blank" rel="noopener">Insulation Calculator — RevenueLab</a> (2026).</p>
Source: [Insulation Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/insulation) (2026).