R-Value and U-Value Insulation Calculator (2024)

Material List	R-Value (up/out)	U-Value (up/out)	R-Value (down/in)	U-Value (down/in)	Thickness
No materials entered yet(see below)
GRAND TOTAL:	R 0.000	1000001.000	R 0.000	1000001.000	0.0mm
Just the insulation:	R 0.000	1000001.000	R 0.000	1000001.000	0.0mm

The R-Value calculator is best used as follows:

Work out all the different materials and surfaces that make up the wall/ceiling or surface you want to work out the R-Values and U-Values for. Remember the horizontal or vertical orientation of the material is important to get its insulation value correct.
Remember to take into account any air boundaries you may have, such as with the outside or with the inside of rooms.
Select the Units of measurement you want to work in, either metric (AU,EU) or imperial (US)
Enter each material or surface into the above R-Value calculator. To get the right depth of a material enter multiples of it tell you get above the required depth.
Note the totals. The up/out values apply mostly to Winter conditions and the down/in values apply mostly to Summer conditions.

Remember, the values calculated here should be taken as a rough guide, as certain materials (i.e. reflective or foil insulation) the total R-Value effect cannot be calculated by straight addition of all the component R-Values.

Also remember, when considering the R-Value of insulation in a built construction, it is often hard to go back and add more insulation after the wall or structure has been built; so err on having slightly more insulation than you need than less insulation.

BTW If you create an account for yourself you can save the materials list you made and come back to them later..

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This calculator is now available as a fully featured Android app, work out R-Values on the move and share - search for R Value Calculator on the Android Market. Or click here if on an Android phone.
Also available on Android is a free Green Dictionary of 800+ Eco & Green terms.

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Related Tags..

energy efficiency, sustainable development, passive solar, insulation, buildings

Comments left

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 AustraliaReply 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 SwedenReply 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 StatesReply 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 ZealandReply 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 KingdomReply 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 StatesReply 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 CanadaReply to this comment
    - stewiesno1 said:
      Just down from the material list.
      Cheers
      ON Sat, 10 Nov 12, 5:27am probably from AustraliaReply to this comment
Avne Vishkin said:
Great.
ON Fri, 7 Sep 12, 3:05am probably from IsraelReply 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 MalaysiaReply 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 KingdomReply 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 StatesReply 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 KingdomReply 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 StatesReply to this comment
Nn said:
hi
ON Tue, 8 Dec 15, 5:30pm probably from CanadaReply 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 AfghanistanReply 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 StatesReply to this comment

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R-Value and U-Value Insulation Calculator (2024)

FAQs

How do you calculate R-value and U-value? ›

To calculate R-value, divide 1 by the U-value figure. For example, a U-value of 0.10 equals an R-value of 10 (1 divided by 0.10). To calculate U-value, divide 1 by the R-value—a 3.45 R-value equals a U-value of 0.29.

See Details ›

What is the U-value of R19 insulation? ›

U-0.055

Explore More ›

What is the U-value of R 21 insulation? ›

R21 Wall Insulation (1/21) is 0.048 U-Value in Imperial terms (USA). If I multiply this value by a factor of 5.678 you get a metric U-value of 0.27.

What is the U-value of R40 insulation? ›

For instance: in cold climates, wall insulation should be R-30 to R-40 (U-value, Metric system: U-0.19 and U-0.14), which requires about 9.5 inches (24 cm) of fiberglass, 7.5 inches (19 cm) of expanded polystyrene, 8 inches (20 cm) of low-density polyurethane or 4.5 inches (12 cm) of polyso.

Tell Me More ›

What is a good U-value for insulation? ›

The best insulating materials have a U-Value of close to zero; the closer to zero the better. Under LABC guidelines, the retrofitting of insulation to existing buildings requires the following U-Value targets: Wall – 0.3 W/m2k. Roof – 0.18 W/m2k.

Is .30 a good U-factor for windows? ›

The best, high-performance, double-pane windows may have a U-factor of 0.30 or lower, indicating that they are very energy-efficient. Some triple-pane windows may have a U-factor as low as 0.15.

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What is the highest R-value for a 2x4 wall? ›

Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products. Generally, batt insulation is the least expensive wall insulation material but requires careful installation for effective performance (see page 4).

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Why is R19 thicker than R21? ›

R19 is 6.5″ thick whereas R21 is 5.5″ thick. Thinner by one inch and yet 2 points higher in R value. The common explanation as to why this is so, is that the R21 insulation is said to be “more dense”.

Learn More Now ›

What R-value is best for insulation? ›

Depending on where you live and the part of your home you're insulating (walls, crawlspace, attic, etc.), you'll need a different R-Value. Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.

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Is R15 or R13 better insulation? ›

R-value is a metric that tells us how well insulation performs at reducing heat loss. When comparing R13 to R15, insulation designated as R15 performs better at reducing heat loss than R13. R-values are generally cumulative, meaning that you can stack two layers of R6 insulation boards to achieve R12.

Keep Reading ›

Does compressing insulation reduce R-value? ›

The North American Insulation Manufacturers Association (NAIMA) says: “When you compress fiber glass batt insulation, the R-value per inch goes up, but the overall R-value goes down because you have less inches or thickness of insulation.”

Learn More ›

Is R60 attic insulation worth it? ›

R60, there's no doubt that R60 will make your house more energy efficient, which in turn saves you significant amounts of energy, lowering your energy bills and making your home more comfortable during the cold months.

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What is the formula for finding R-value? ›

r = ∑ ( x i − x ¯ ) ( y i − y ¯ ) ∑ ( x i − x ¯ ) 2 ∑ ( y i − y ¯ ) 2 . Label your variables x and y as it is easier to work with letters compared to names of variables.

How do you calculate the value of R? ›

The value of R at atm that is at standard atmospheric pressure is R = 8.3144598 J. mol^-¹. K^-¹.

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How do you convert metric U-value to R-value? ›

To get from metric U-value to American R-value:

Multiply the U-value by 0.176. At this point, the units will remain the same, Watts per Kelvin meters squared. For example, begin with a U-value of 0.247 Watts per Kelvin meters squared. ...
Divide 1 by 0.043472 which gives you (1/0.043472) = 23.0 American R-value.