Insulation Calculator
Packs needed and cost to insulate any attic, wall, or floor area.
What it does
Insulation buying starts from net area divided by pack coverage. Measure the attic or wall surface, add a share for cuts around joists and openings, then round up to whole packs because stores do not split them.
The tool above runs imperial and metric side by side. Enter area with the coverage printed on the pack for your thickness, add waste percent, and optionally a price to see the material cost.
The default covers 1000 ft² with 88 ft² packs and 10% waste: 1100 ft² of material in 13 packs for $780.00 at $60 each. The metric mirror of 92.9 m² with 8.18 m² packs lands on the same 13 packs.
DOE insulation guides and Energy Star sealing pages both pair coverage math with R value targets by climate zone. Buy the area here, then pick the R value the zone table names for attics, walls, and floors.
How to use
- Pick imperial or metric to match your tape and pack labels.
- Enter the net area to insulate, one surface at a time.
- Enter the pack coverage for the thickness you will install.
- Add waste percent for cuts, usually 10, more for chopped layouts.
- Read packs first, then material and cost. Buy all packs from one lot.
Formula
- area
- Net surface to cover in ft² or m².
- coverage
- Area one pack covers at the chosen thickness.
- waste
- Cut share around joists, wires, and openings.
Coverage belongs to a thickness: the same pack covers less area at higher R value. Always read the coverage line for the exact product and depth you plan, never a generic brand number.
Worked example
Example: 1000 ft² attic, 88 ft² packs, 10% waste
Imperial defaults: area 1000, coverage 88, waste 10, price 60.
- Material: 1000 x 1.10 = 1100 ft².
- Raw packs: 1100 / 88 = 12.5.
- Round up: 13 packs (stores sell whole packs).
- Cost: 13 x 60 = $780.00.
- Tool shows 13 packs, 1,100 ft², $780.00.
Reference table
| Zone winters | Attic target | Cavity note |
|---|---|---|
| Warm (zones 1-2) | R30 to R49 | Air seal first |
| Mixed (zones 3-4) | R38 to R60 | Seal plus R38 typical |
| Cold (zones 5-8) | R49 to R60 | Deep fill wins |
| Walls everywhere | R13 to R21 | Cavity depth sets it |
Limits
- Area math only. R value targets come from the zone table and local code.
- Framing share, ducts, and recessed lights need their own allowances.
- Compressed batts lose R value; depth must stay full.
- Wet or moldy cavities need repair before any new fill.
Common mistakes
- Using coverage for the wrong thickness from the same brand.
- Skipping waste on chopped attics with many penetrations.
- Stuffing batts tight instead of cutting to fit loosely.
- Leaving air gaps at eaves and hatches that bypass the fill.
- Mixing products of different depths in one layer.
Try it yourself
Quick checks. Answers sit tucked under each question.
500 ft² at 88 ft² a pack, no waste?
500 / 88 = 5.68, so 6 packs.
92.9 m² at 8.18 m² a pack, 10% waste?
92.9 x 1.10 = 102.19 m², / 8.18 = 12.49, so 13 packs.
13 packs at $60?
13 x 60 = $780.00.
Questions
How many packs do I need?
Area times waste factor divided by pack coverage, rounded up: 1000 x 1.10 / 88 = 13 packs.
What waste percent?
About 10% for open attics, more for cut up walls and dormers.
Does thickness change packs?
Yes. The same product covers fewer ft² at higher R, so read the line for your depth.
R value or area first?
Zone sets R value, area sets packs. This page counts packs; the table sketches targets.
Can I mix leftover packs?
Same depth and facing only, and keep one lot per layer for even fill.
What is missing from cost?
Vapor barrier, baffles, hatches, sealing, and tools. This page prices packs alone.