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# > R-Value to U-Value Conversion Calculator

R-value is how well a particular construction material insulates, the higher the better. Whereas the lower the U-Value, the more energy efficient the material is. This calculator makes it easy to convert between R and U Values. The U-value is the reciprocal of the R-value; that is U = 1/R and R = 1/U.

Values to convert

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• Apsara2011 said:

what are and how can I draw the junctions of wall fabric with the building structure?

ON Thu, 19 May 11, 2:46am probably from Australia  Reply to this comment

• Naturlig Canuck said:

with a few changes the adroid app could be quite usefull. 50 materials in the list is just way too limiting. If I'm really list the materials used in the wall or roof, tell me what the thermal conductivity is, let me enter the thickness. Then the app calculates the resulting u-value and adds it all together. check out this website for inspiration:-) http://www.vesma.com/tutorial/uvalue01/uvalue01.htm

ON Fri, 20 May 11, 7:10am probably from Sweden  Reply to this comment

• Eco Guy said:

The app is going through some improvements atm... I'll look at that and see if I can fit it in. Also you can add your own materials as required.

ON Mon, 26 Sep 11, 2:56am probably from United States  Reply to this comment

• Insulduude said:

Is there a chance you would look at an app for iphone ipad? if not already available?

Thanks

ON Sun, 11 Dec 11, 7:26pm probably from New Zealand  Reply to this comment

• Mike said:

Your calculator ignores the SI units versus SAE units. If someone types in the R-value from the US, which is typically SAE units, they get the wrong answer in U-value. You should fix this and/or have a toggle for people to convert. Here's the values from Wiki: The conversion between SI and US units of R-value is 1 h•ft²•°F/Btu = 0.176110 K•m²/W, or 1 K•m²/W = 5.678263 h•ft²•°F/Btu

ON Mon, 6 Feb 12, 11:32am probably from United Kingdom  Reply to this comment

• Eco Guy said:

There is an imperial and metric switch you can use for this.

ON Mon, 2 Apr 12, 11:47pm probably from United States  Reply to this comment

• Andrew said:

Eco Guy: where is the switch? I was pulling my hair out at the erroneous calculations! This definitely needs to be fixed, as it discredits an otherwise brilliant array of tools.

ON Sun, 13 May 12, 3:41pm probably from Canada  Reply to this comment

• Avne Vishkin said:

Great.

ON Fri, 7 Sep 12, 3:05am probably from Israel  Reply to this comment

• HGTay said:

To use the R-value calculator, how to enter the new material list??

ON Thu, 20 Dec 12, 5:48am probably from Malaysia  Reply to this comment

• Phil said:

How can you calculate a U Value from an R value.

Doesn't a U value represent the reciprocal of several R Values? Isn't this calculating a K value from the R value??

ON Fri, 26 Apr 13, 9:45am probably from United Kingdom  Reply to this comment

• Waldemar said:

how to convert US value R30 to Europe W/m2 K ?

ON Mon, 23 Dec 13, 5:51pm probably from United States  Reply to this comment

• Fernando said:

I was given an R-Value as 0.26 (m2K)/W for a particular material and I need to convert to U-Value which is expressed as W/m2K. Could you help? Thanks Fernando

ON Mon, 20 Jan 14, 11:04am probably from United Kingdom  Reply to this comment

• Greg said:

Doesn't work! Trying entering .088 for the U value.

ON Fri, 9 May 14, 1:42pm probably from United States  Reply to this comment

• Nn said:

hi

ON Tue, 8 Dec 15, 5:30pm probably from Canada  Reply to this comment

• Hafizullah said:

Dear Mr/Madam, Have a nice day, 1-How can find density of foam rigid insulation for R- Value, what is the equation between R- Value and density? 2-How can find R-Value? If passable send me calculation.

ON Mon, 22 Jan 18, 1:41pm probably from Afghanistan  Reply to this comment

• Luis Salazar said:

WHAT IS THE R VALUE THROUGH A 2 X 4 WOOD STUD AT THE 3 1/2 INCH ?

ON Wed, 14 Feb 18, 5:43pm probably from United States  Reply to this comment