Honey-Do Squad mascotHoney-DoSquadMy List

Insulation Calculator

Bags of fiberglass batts by area and R-value.

Batt bags
14 bags
Area
500 sq ftR-13 batts
Insulation to buy
550 sq ftincludes 10% waste
Batt bags
14 bags~40 sq ft per bag (check label)
Cost (est.)
$303~$0.55/sq ft for R-13
Doing this for work? Estimate the whole job in minutes.
JRIQ turns plans and site photos into full material + labor estimates with AI — built by the team behind these calculators.
Try it free →

Fiberglass batt insulation is a cheap, high-payback DIY upgrade — warmer rooms, lower bills. The whole game is a snug, complete fill: batts cut to fit, no gaps, no compression, and the right R-value for your climate.

DifficultyBeginner
TimeA few hours per room of walls; an attic is a longer day
SkillsEasy work, but wear protection — fiberglass itches and irritates lungs
PermitsNew insulation is usually inspected as part of permitted work; codes set minimum R-values by area of the house.

Tools you'll need

Step by step

  1. Pick the right R-valueMatch R-value to the cavity and your climate — roughly R-13/R-15 for 2×4 walls, R-19/R-21 for 2×6 walls, and R-38–R-49 in attics.
  2. Cut batts to fit snugMeasure each bay and cut batts slightly long so they friction-fit with no gaps at the top, bottom, or sides.
  3. Don't compress itFluff batts to fill the cavity full depth. Compressed insulation loses R-value — split batts around wires and pipes instead of crushing them.
  4. Get the vapor side rightIf using faced batts, face the paper toward the heated (living) side in cold climates. Don't double up vapor barriers.
  5. Fill the gapsStuff small gaps around boxes and use canned foam at penetrations — the little voids are where heat escapes.

Common mistakes

Compressing the batts
A compressed R-19 performs like an R-13. Fill the cavity to full depth and split around obstacles.
Leaving gaps and voids
Cut batts to fit each bay snugly — gaps around wires, boxes, and edges leak heat.
Vapor barrier on the wrong side
In cold climates the facing goes toward the living space; never sandwich insulation between two vapor barriers.

Safety

Frequently asked questions

How much insulation do I need?
Enter the area and R-value above — the calculator adds 10% waste and returns bags of batts.
What R-value should I use?
Roughly R-13/R-15 in 2×4 walls, R-19/R-21 in 2×6 walls, and R-38–R-49 in attics — check your local code minimums.
Faced or unfaced batts?
Faced (with a vapor retarder) for exterior walls and where no barrier exists; unfaced for adding to existing insulation or interior sound-proofing.

Next steps for this project

Drywall
How many drywall sheets, mud, and tape a room needs — walls and ceiling.
Vapor Barrier
Rolls of 6-mil poly sheeting for under a slab, deck, or crawlspace.
Siding
Squares of vinyl siding and house wrap for a home.

Sources & references

Popular Insulation sizes

Insulation for 200 sq ft (R-13)Insulation for 200 sq ft (R-30)Insulation for 300 sq ft (R-13)Insulation for 300 sq ft (R-30)Insulation for 400 sq ft (R-13)Insulation for 400 sq ft (R-30)Insulation for 500 sq ft (R-13)Insulation for 500 sq ft (R-30)Insulation for 600 sq ft (R-13)Insulation for 600 sq ft (R-30)Insulation for 800 sq ft (R-13)Insulation for 800 sq ft (R-30)Insulation for 1000 sq ft (R-13)Insulation for 1000 sq ft (R-30)Insulation for 1200 sq ft (R-13)Insulation for 1200 sq ft (R-30)Insulation for 1500 sq ft (R-13)Insulation for 1500 sq ft (R-30)Insulation for 2000 sq ft (R-13)Insulation for 2000 sq ft (R-30)