How this site is built
Review the calculation methodology to see which figures are exact geometry, which depend on material assumptions, and which figures have recorded sources. The source registry records every cited figure and its review status.
How the insulation calculator works
This is a coverage count from net wall area and the entered batt face size. It rounds to whole batts after the cut allowance.
It does not select R-value, material type, vapour control or assembly details. Those choices depend on the building assembly and local requirements.
Formula used for insulation calculator
The calculator keeps the measured quantity separate from any purchase rounding or allowance.
- Net wall
gross wall area − openings - Batt face
batt width × batt length - Count
net wall × allowance ÷ batt face, rounded up
Planning choices for insulation calculator
| Situation | Use | Why it matters |
|---|---|---|
| Regular stud bays | Use batt dimensions | Count aligns with repeated cavities |
| Irregular framing | Use package coverage plus layout | Short cavities create offcuts |
| Loose-fill or spray product | Use manufacturer coverage | Batt count is the wrong purchase model |
These are measurement and ordering choices, not structural specifications or code requirements.
Measure and order insulation
Use the actual cavity count and dimensions when framing is irregular. Area is a planning shortcut, not a substitute for a bay schedule.
Match product width to the framing spacing and use the package coverage for final purchasing. Do not compress batts to force a fit.
Insulation Calculator questions
Does this choose an R-value?
No. It estimates quantity only.
Can I use it for attic loose fill?
No. Use the manufacturer’s bag-coverage chart for target depth and installed density.
Why subtract openings?
Large doors and windows remove cavities, but add a cut allowance for framing details around them.
Variables and units
For the default “Wall area” mode. Other modes label their own fields in the calculator.
length- Total wall length: ft, in, yd, m, cm.
height- Wall height: ft, in, yd, m, cm.
openingWidth- Typical opening width: ft; optional.
openingHeight- Typical opening height: ft; optional.
openingCount- Number of openings: unitless; optional.
sheetWidth- Sheet or batt width: ft.
sheetLength- Sheet or batt length: ft.
waste- Cut allowance: %; optional.
Worked example: 48 ft of 8 ft exterior wall
An exterior wall run is 48 ft by 8 ft with two 3 ft by 5 ft openings and 16 in by 8 ft batts.
| Field | Value |
|---|---|
| Total wall length | 48 ft |
| Wall height | 8 ft |
| Typical opening width | 3 ft |
| Typical opening height | 5 ft |
| Number of openings | 2 |
| Sheet or batt width | 1.333 ft |
| Sheet or batt length | 8 ft |
| Cut allowance | 8 % |
| Result | Value |
|---|---|
| batts to buy | 36 batts |
| Net wall area | 354 ft² |
These figures are generated by the same calculation the calculator above uses, so they update automatically if the method changes.
Where these numbers come from
This calculator uses geometry and values shown in the form. Editable product dimensions, coverage figures, prices and allowances are inputs, not universal recommendations; confirm them against the product label, drawing or supplier quote.
Content release:
Published by Material Totals. Review the methodology and source assumptions.
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