The Case of “R Value” vs. “U Value” of Glass

Question: What is the “R-Value” of Glass?

Glass Detective,

Can you tell me how to calculate the “R-Value” of glass based on its “U-Value”? I have an issue with a building inspector in my town based on energy codes, and my wall area must achieve a certain overall “R-Value” for me to get a certificate of occupancy permit. I have “R-Values” for everything but the glass. The glass company that put the glass in can only tell me the “U-Value” which they said is 0.29. According to the label on the glass when it was installed, the glass is an insulated unit of Solarban 60 with Low-E. Does any of this make sense to you, and if so, how do I get an “R-Value” for this glass?

Thank you,

Dave R.




This whole “U-Value” vs. “R-Value” thing can be a little confusing. For many years now, most of the glass manufacturers have provided “U-Values” only. However, the conversion, or glass “R-Value” calculator if you will, is pretty simple. You see, “U-Values” and “R-Values” are the reciprocals of each other. Remember those old high school math classes? We were taught that to get any number’s reciprocal, you simply divide 1 by that number. So the reciprocal of your glass unit’s “U-Value of 0.29 can be determined by dividing the number 1 by 0.29 which would give us 3.4482 or roughly 3.5 and that would be the “R-Value” for your glass. If you had a product’s “R-Value” and wanted to know its “U-Value” the process would get reversed … divide the number 1 by its “R-Value” and you would have its “U-Value.” I really hope this helps and thank you for reaching out!

-Glass Detective

Read More attempts to provide accurate information but cannot be held liable for any information provided or omitted.  You should always work with a licensed, insured and reputable glass shop that can assess your specific needs and local building codes and offer professional services. Never attempt to cut, install, or otherwise work with glass yourself. All content is provided on an informational basis only.

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Lyle Hill

By Lyle Hill

Lyle Hill has been in the glass and metal industry for more than 40 years. In this time he has managed glass retail, contract glazing, mirror, architectural window, window film, and automotive glass businesses throughout America. He obtained an MBA from IIT with a focus on Technology and Engineering Management.

Hill is also a columnist for glass industry trade magazines and often called the “face” of the glass industry. He has also authored books including “The Broken Tomato and Other Business Parables,” which is available through Amazon.

One response to “The Case of “R Value” vs. “U Value” of Glass”

  1. We have glass labeled: Anthony Tempered Glass, ANSI Z97.1.2015, 16 CFR 1201 CLL, SGCC 6099 5/32 UA
    With this informaiton, could you tell me what the R value of this glass is?

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