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Insulation calculator

You are buying coverage, not a vibe. Batts list sq ft per bag or bundle; blown products list bags per sq ft at a target R-value. This page turns wall or floor area into a bag/batt count with waste so you leave the store once. Pick area (or L×W), enter coverage from the package, set waste. For attic depth and blown fills, the attic page is tighter.

ft
ft
sq ft
Optional
sq ft
From bag label
8%
0510152025

+8% so you don't come up short

ORDER ESTIMATEINSULATION
Packs to buy11
Order area432 sq ft
Net area400 sq ft
Waste8%
How it calculates
packs = ceil(area × (1 + 8%) ÷ coverage sq ft per pack).

Estimate only — not a contractor bid. Confirm bag yields and local codes before you pour or order.

When to use

Garage wall batts; basement rim joists; a single-room remodel; comparing two bag sizes on the shelf.

When not to

Whole-house Manual J / load calculations. Spray foam board-foot or kit yield charts with weird expansion — use the kit. Open attics with inches of blown depth → attic insulation calculator.

Assumptions

Coverage = sq ft per bag/batt pack you enter from the label. Waste default 5–10% (cuts around boxes and wiring). R-value is a product choice; the calculator does not convert climate zone charts into code compliance.

Worked examples

Example 1

400 sq ft of 2×4 wall, R-13 batts covering 40 sq ft/pack, waste 8%
→ order 432 → 11 packs

Split cavities and plumbing chases eat extras.

Example 2

120 sq ft floor over a crawl, packs cover 50 sq ft, waste 5%
→ 3 packs

Compression against ducts kills R — count area, then install without crushing.

How it calculates

Area ÷ label coverage with waste, round up packs.

  1. Enter wall or floor area (or L×W).
  2. Enter coverage sq ft per pack from the label.
  3. Set waste; read packs.
net area (sq ft)
order area = net × (1 + waste%)
bags/packs = ceil(order area ÷ coverage_per_pack)

Common traps

  1. Label coverage wins — same “R-19” SKUs differ by bag.
  2. Faced vs unfaced is fire/vapor detailing, not a different area formula.
  3. Do not mix leftover thicknesses hoping R averages out.
  4. Electrical boxes — cutouts waste more than the % slider admits on small walls.

Next tool

Attic blown or depth-based → attic insulation calculator.

After walls close, drywall → drywall calculator.

FAQ

Area ÷ coverage per bag, add waste, round up.

Related

Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.