R-Value Calculator
Total assembly R-value and U-factor from your layers.
Enter your values
Enter the insulation r-value you are working with.
Enter the sheathing r-value you are working with.
Enter the cladding + finishes r-value you are working with.
Enter the air films r-value you are working with.
Enter the area in sq ft.
Enter the temperature difference in F.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Total R-value
- R-26.35
- U-factor
- 0.038 BTU/hr-ft2-F
- Heat loss
- 1,214 BTU/hr
- Per square foot
- 1.52 BTU/hr-ft2
Working
- 1R 26.35 -> U 0.038 x 800 ft2 x 40 F = 1,214 BTU/hr
Quick answer
R-values of layers in series simply add. U-factor is 1/R total, and heat loss per square foot is U x temperature difference.
R total = sum of layer R; U = 1/R; Q = U x A x deltaT
At a glance
| What it does | Total assembly R-value and U-factor from your layers. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Insulation R-value, Sheathing R-value, Cladding + finishes R-value, Air films R-value, Area, Temperature difference |
| Main output | Total R-value |
| Formula | R total = sum of layer R; U = 1/R; Q = U x A x deltaT |
| Cost | Free — no sign-up, no download |
How to use the R-Value Calculator
- 1List every layer of the assembly and enter its R-value.
- 2Include interior and exterior air films (about 0.85 combined for walls).
- 3Compare the total against your climate zone's code minimum.
Inputs explained
- Insulation R-value
- Enter the insulation r-value you are working with.
- Sheathing R-value
- Enter the sheathing r-value you are working with.
- Cladding + finishes R-value
- Enter the cladding + finishes r-value you are working with.
- Air films R-value
- Enter the air films r-value you are working with.
- Area(sq ft)
- Enter the area in sq ft.
- Temperature difference(F)
- Enter the temperature difference in F.
Worked example
Using the values the calculator loads with:
Inputs
- Insulation R-value19
- Sheathing R-value5
- Cladding + finishes R-value1.5
- Air films R-value0.85
- Area800 sq ft
- Temperature difference40 F
Results
- Total R-valueR-26.35
- U-factor0.038 BTU/hr-ft2-F
- Heat loss1,214 BTU/hr
- Per square foot1.52 BTU/hr-ft2
- R 26.35 -> U 0.038 x 800 ft2 x 40 F = 1,214 BTU/hr
Frequently asked questions
Do R-values really just add?
In series, yes. But studs bridge the insulation, so a real wall performs 10 to 25% worse than the cavity number unless you add continuous exterior insulation.
What R-value do I need?
Typically R-13 to R-21 walls and R-38 to R-60 attics in the US, depending on climate zone. Check your local energy code.
What do I need to enter into the R-Value Calculator?
Just 6 values: insulation r-value, sheathing r-value, cladding + finishes r-value, air films r-value, area, temperature difference. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the R-Value Calculator work out the answer?
R-values of layers in series simply add. U-factor is 1/R total, and heat loss per square foot is U x temperature difference. It applies the formula R total = sum of layer R; U = 1/R; Q = U x A x deltaT and shows the working so you can check each step by hand.
Is the R-Value Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.