What R-value do I need?

R-value requirements vary by climate zone. As a general guide: attics need R-38 to R-60, walls R-13 to R-21, and floors R-25 to R-30. Check the U.S. Department of Energy climate zone map or your local building code for the exact requirement in your area.

What is the difference between batts and loose-fill?

Batts (rolls) are pre-cut or continuous blankets of fiberglass or mineral wool that fit between studs or joists. Loose-fill (blown-in) consists of small fibers or particles blown into place, ideal for attics and irregular cavities. Loose-fill is measured in bags, each covering a stated square footage at a given depth.

How much waste factor should I add?

A 10% waste allowance is standard for straightforward rectangular areas. Add 15% for spaces with many obstructions (pipes, beams, outlets) and up to 20% for attics with complex framing or multiple valleys.

Does this calculator handle metric measurements?

The calculator uses square feet matching North American product labeling. To convert square meters to square feet, multiply by 10.764 (e.g., 50 m² x 10.764 = 538 sq ft).

How is coverage per unit determined?

Coverage is printed on the product label — it states the area (sq ft) one roll, batt, or bag covers at a specific depth/R-value. Always match the labeled R-value to your target before buying.

Why is the sheet count rounded up?

You must purchase whole units (rolls, batts, or bags). Partial units cannot be returned in most cases, so the calculator always rounds up to ensure you have enough material.

Insulation Calculator

Name: Insulation Calculator
Availability: InStock
Author: Nham Vu

Calculate how many rolls, batts, or bags of insulation you need for walls, floors, or attics based on area and insulation type, with an R-value reference table.

Inputs

Area to Insulate (sq ft)

Insulation Type

Coverage per Unit (sq ft)

Waste Allowance (%)

10% standard; 15–20% for complex areas.

Price per Unit ($) (optional)

Results

Enter area and press Calculate

R-Value Quick Reference

Recommended minimum values per DOE climate zones 3–6 (most of the continental U.S.).

Location	Min R-Value	Common Product
Attic (unfinished)	R-38 – R-60	Blown-in or thick batts
Cathedral ceiling	R-30 – R-38	Deep-cavity batts
Exterior wall (2x4)	R-13 – R-15	Standard fiberglass batt
Exterior wall (2x6)	R-19 – R-21	Wide batt or mineral wool
Floor over unheated space	R-25 – R-30	Floor batts with vapor barrier
Crawl space wall	R-10 – R-19	Rigid board or batt

Summary

Calculate how many rolls, batts, or bags of insulation you need for walls, floors, or attics based on area and insulation type, with an R-value reference table.

How it works

Select the installation location: wall, floor, or attic.
Enter the total area to insulate in square feet.
Choose your insulation type (fiberglass batts, mineral wool batts, or loose-fill).
Select the product coverage per roll, batt, or bag from the dropdown, or enter a custom value.
Add a waste allowance (10% recommended) and an optional price per unit.
Click Calculate to see units needed, total R-value, and estimated cost.

Use cases

Planning attic insulation before winter to reduce heating bills.
Estimating wall batt count for a new-build or renovation.
Comparing roll vs. loose-fill bag quantities for the same area.
Budgeting insulation material cost before visiting a home center.
Verifying your planned R-value meets local energy code requirements.
Calculating floor insulation for a crawl space or over a garage.
Generating a quick material takeoff for a contractor bid.
Teaching students or apprentices how insulation quantities are estimated.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu