Insulation Calculator

Enter the area, your target R-value and any existing insulation. Bag or roll counts come from the coverage printed on your product — it varies too much between products to assume.

Tapeline — Insulation Calculator

Printed October 9, 2026

Area to insulate1000 sq ft
Target total R-value49
Existing R-value0
MaterialLoose-fill cellulose (≈ R-3.5/in)
Custom R per inch3.5
Coverage per bag or roll at this R0 sq ft

Results update as you type.

ENERGY STAR and DOE publish recommended R-values by climate zone.

Estimate from existing depth × R per inch.

Typical values; product R-values vary. Use the label value when you have it.

Used only when Material is Custom.

sq ft

From the product label or coverage chart. Leave 0 to skip bag count.

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Watch the step-by-step video

Watch it explained

A step-by-step video using your numbers: what to enter, what the result means, and a “what if” example. On-screen instructions follow each step as it happens.

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What the animation shows

The animation and the step-by-step video above use your numbers. Here is the same walkthrough written out for the default example.

Finished frame of the insulation calculator animation for the default example
The last frame of the animation for the default example.

What you enter

  • Area to insulate: 1000 sq ft.
  • Target total R-value: 49. ENERGY STAR and DOE publish recommended R-values by climate zone.
  • Existing R-value: 0. Estimate from existing depth × R per inch.
  • Material: Loose-fill cellulose (≈ R-3.5/in). Typical values; product R-values vary. Use the label value when you have it.
  • Coverage per bag or roll at this R: 0 sq ft. From the product label or coverage chart. Leave 0 to skip bag count.

What happens, step by step

  1. A blower hose spreads loose-fill cellulose evenly between and over the joists.
  2. With no insulation yet, all R-49 has to be added.
  3. Now it covers the joist tops, so heat cannot slip through the wood.
  4. At R-3.5 per inch, 14 in reaches the R-49 line.

The answer: added thickness needed is 14 in.

How it’s calculated

  • R to add = target R − existing R
  • Thickness (in) = R to add ÷ R per inch
  • Bags = area ÷ coverage per bag at the target R

Worked example

1,000 sq ft attic with R-11 existing, target R-49, cellulose.

Inputs

Area to insulate
1000 sq ft
Target total R-value
49
Existing R-value
11
Material
Loose-fill cellulose (≈ R-3.5/in)
Custom R per inch
3.5
Coverage per bag or roll at this R
0 sq ft

Results

Added thickness needed
10.9 in
R-value to add
38
R per inch used
3.5

Load this example into the calculator

Assumptions and limits

  • R per inch values are typical mid-range figures; installed performance depends on density and installation quality.
  • Loose-fill settles; manufacturer coverage charts already account for settled thickness.
  • No claim is made about energy savings — that depends on climate, air sealing and the rest of the building.

Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.

Questions

How deep should attic insulation be?

For R-49 with cellulose at about R-3.5 per inch, roughly 14 in total. Fiberglass loose-fill needs more depth for the same R.

Does more insulation always save money?

Returns diminish as R-value increases, and air sealing often matters as much. Savings depend on climate, fuel prices and the existing house.