Quick answer
Total R-value is the sum of the layers' R-values, and the U-value is 1 ÷ R. Layers of R-0.17, R-13 and R-0.45 total R-13.62 with a U-value of 0.0734.
Enter the R-value of each layer, separated by commas. The calculator returns the total R and U. Use this insulation r-value calculator to check your own figures.
Related tools: P-Value Calculator: P-value from a z, t, chi-square or F statistic. Present Value Calculator: Today's value of a future amount at a given discount rate. Coin Value Converter: Convert pennies, nickels, dimes and quarters to dollars and back.
How to use the Insulation R-Value Calculator
- Type r-value of each layer, for example 0.17, 13, 0.45.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| R-value of each layer | Text, such as 0.17, 13, 0.45 | — |
Formula and method
Formula
R_total = Σ R_layer; U = 1 ÷ R_total
IEEE-754 double precision; shown to the decimals indicated.
Valid for layers in series with no thermal bridging; framing, gaps and moisture reduce real performance. Use the R-values given by the manufacturer for each layer. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: R-value of each layer = 0.17, 13, 0.45.
| Result | Value |
|---|---|
| Total R-value | 13.62 |
| U-value (1 ÷ R) | 0.0734 |
Example 2
Inputs: R-value of each layer = 3.7, 19, 0.68, 0.17.
| Result | Value |
|---|---|
| Total R-value | 23.55 |
| U-value (1 ÷ R) | 0.0425 |
Example 3
Inputs: R-value of each layer = 30.
| Result | Value |
|---|---|
| Total R-value | 30 |
| U-value (1 ÷ R) | 0.0333 |
The first line is the headline result (total R-value). Below it the insulation R-Value Calculator lists u-value (1 ÷ R), which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Series layers add
Heat flows through the layers in series, so resistances add: air film, insulation and drywall might be 0.17 + 13 + 0.45. U is the rate of heat flow, so a lower U means a better-insulated wall.
Real walls leak more
Framing, fasteners and gaps create thermal bridges that lower the effective R-value below the sum. A wall with R-13 batts between studs may deliver R-11 overall. Use the result for comparison, not for code compliance.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- R-value of each layer: left empty shows "Enter r-value of each layer." beside that field and no result.
Choosing between the Insulation R-Value Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [P-Value Calculator](/statistics/p-value/) | test statistic, statistic value and test type | p-value |
| [Present Value Calculator](/finance/present-value-calculator/) | future value, annual discount rate and years | Present value |
| [Coin Value Converter](/converters/coin-value-converter/) | value, from and to | Pennies (1¢) → Dollars ($1) |
| [Critical Value Calculator](/statistics/critical-value/) | distribution, significance level and tails | Critical value |
| [Expected Value Calculator](/statistics/expected-value/) | values and probabilities | Expected value E[X] |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Thermal bridging lowers effective R-value
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for r-value of each layer to confirm this.
Frequently asked questions
What does R-value measure?
Resistance to heat flow; higher is better.
What are the US units?
In US units R-value is ft²·°F·h/Btu; in SI it is m²·K/W.
Does adding layers always help?
Yes in series, but air gaps and moisture matter.
What does the Insulation R-Value Calculator calculate?
Total R-value and U-value of layers in series. It returns Total R-value and U-value (1 ÷ R).
What formula does the Insulation R-Value Calculator use?
R_total = Σ R_layer; U = 1 ÷ R_total. Valid for layers in series with no thermal bridging; framing, gaps and moisture reduce real performance.
What do I need to enter in the insulation R-Value Calculator?
You enter R-value of each layer.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Thermal bridging lowers effective R-value.
What is an example of a insulation R-Value result?
With r-value of each layer 0.17, 13, 0.45, the total R-value is 13.62.
Where does the method come from?
The method follows: Standard series thermal-resistance relation (ASHRAE Handbook—Fundamentals).
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Thermal bridging lowers effective R-value.
Related calculators
- P-Value Calculator — P-value from a z, t, chi-square or F statistic.
- Present Value Calculator — Today's value of a future amount at a given discount rate.
- Coin Value Converter — Convert pennies, nickels, dimes and quarters to dollars and back.
- Critical Value Calculator — Critical values for z, t, chi-square and F distributions.
- Expected Value Calculator — Expected value and variance of a discrete distribution.
- Absolute Value Calculator — Absolute value of a number.
Sources
- Standard series thermal-resistance relation (ASHRAE Handbook—Fundamentals)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.