U-Value & R-Value Converter
Ver en españolU-value is the inverse of R-value, and metric RSI is a different scale again. Enter one number and get all of them, plus the totals for a layered assembly.
Your project
Your results
- R-value (imperial)
- R-19
- U-value (imperial)
- 0.0526
- BTU/hr·ft²·°F
- RSI (metric R)
- 3.346
- m²·K/W
- U metric
- 0.299
- W/m²·K
- Layer 2 adds
- R-6
- Polyiso rigid foam board
- Assembly total with air films
- R-25.85
- Includes R-0.85 for interior and exterior air films
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
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Gear for this job
Rigid Foam Board Insulation
BULLET TOOLS 7 1/4 Inch Circular Rigid Foam Blade, Foam Saw Blade
$70.48
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Pangda 6 Pack Foam Board Insulation Waterproof Shower Wall Panels 48" x 32" x 1/2" Rigid Xps Foam Insulation Board with Fiberglass Mesh for Tile Backer Bathroom Wall & Floor
$209.99
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Ardex TLT 119 Waterproof Cementitious XPS Foam Board 32"x48"x1/2", 5pc
$170.21
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Fiberglass Batt Insulation R19
Infrared Thermometer Gun
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Prices as of Oct 11, 2026, 4:41 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How this calculator works
- U = 1 ÷ R (and R = 1 ÷ U)
- RSI = R × 0.1761
- Assembly R = sum of every layer's R, plus air films
Frequently asked questions
Is a lower U-value better?
Yes. U measures heat that gets through, so lower is better — the opposite of R-value, where higher is better.
Why is metric R-value so much smaller?
Different units. R-19 imperial is RSI 3.35 metric. Multiply imperial R by 0.1761 to convert.
How do I convert R-value to U-value?
U equals 1 divided by R, in the same unit system. R-20 is U-0.05. The catch is which R you start from: the R of the insulation alone is not the R of the assembly, so converting a batt rating gives a U-value better than the wall will ever achieve.
What is RSI and how does it relate to R-value?
RSI is the metric equivalent, in square-metre-kelvins per watt. Multiply an imperial R-value by 0.1761 to get RSI, so R-20 is about RSI 3.52. Canadian and European specifications use RSI, which is why a product can appear to have wildly different ratings in different markets when it is the same material.
Why do windows use U-value instead of R-value?
Convention, mostly, plus the fact that window performance is dominated by the frame, spacer and glazing as a system rather than by a thickness of material. Since U-values are small numbers where lower is better, they compare window assemblies more conveniently than the fractional R-values would.
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R-value (imperial)
R-19