R-Value Calculator
R-value measures resistance to heat flow — higher is better. Pick your material and thickness to see the R-value you get, then compare it against the recommended level for your climate zone.
Your project
Your results
- R-value achieved
- R-15
- Recommended for your zone
- R-60
- Shortfall
- R-45 short
- Extra thickness needed
- 18 in more
- U-value
- 0.0667
Blown-in fiberglass at R-2.5/inch
U = 1 ÷ R
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
Gear for this job
Fiberglass Batt Insulation R19
Owens Corning R-19 Unfaced Fiberglass Insulation 77.5 Sq.ft (15 in x 93 in) 1 Batt
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Owens Corning R-19 Fiberglass Batt Insulation Fits 2x6 Floor or Walls a Total of 10 Bags and Square Footage of 775 FT
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Owens Corning R-19 Unfaced Fiberglass Insulation 128-sq ft (24-in W x 96-in L)
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Rigid Foam Board Insulation
Multi Purpose XPS Foam Board,2 Pack 15.6x11.7X 2in Polystyrene Craft Foam Sheets,Rigid and Easy to Shape,DIY Modeling Art Projects, Party Decoration, Cosplay Prop Production, Carve,Heat Insulation
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Double-Layer Insulated Foam Panels, 3-Pack Insulation Seal Panels for Portable AC Window Vent Seal Kit, Thick Adjustable Insulation Board, Air Conditioner Window Gap Filler
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GCGOODS Window Air Conditioner Insulated Foam Panels, Winter Surround Insulation Side Panel with Top Seal Strip for Window AC Unit Indoor, White
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Thermal Leak Detector Infrared
BLACK+DECKER Thermal Leak Detector (TLD100)
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Flir One - Thermal Imaging Camera for iOS Smartphones (iPhone 14 and Older w/Lightning Port), 240x180 Super Resolution (80x60 Native IR)
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Elitech HVAC Refrigerant Leak Detector 10 Yrs Infrared Sensor Life, Halogen Freon Sniffer, Air Conditioning Detection, Automotive Gas Finder, ILD-200
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How this calculator works
- R-value = R-per-inch × installed thickness
- Shortfall = recommended R − achieved R
- Extra inches = shortfall ÷ R-per-inch
- U-value = 1 ÷ R-value
Frequently asked questions
What R-value do I need in my attic?
Most of the US lands between R-49 and R-60 for attics. Warm southern zones can stop at R-30 to R-49; anything from the Midwest north should target R-60.
Does doubling the thickness double the R-value?
For batts and boards, essentially yes. Loose-fill settles, so blown products lose a little R over time — buy to the coverage chart depth, not the bare minimum.
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R-value achieved
R-15