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The assembly's total thermal resistance.
Add the R-values of every layer, including air films, not just the insulation. A wall is more than its batt: sheathing, cladding, plasterboard and the surface films all contribute.
U-value
0.05263 BTU/hr·ft²·°F
U = 1 ÷ R. The two are exact reciprocals of one another. R-values add across layers; U-values do not. Sum R first, then take the reciprocal once.
They open the calculator with your figures already in it
R-Value to U-Value Calculator: 0.0526 BTU/hr·ft²·°F — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Thermal transmittance is the reciprocal of thermal resistance: U = 1 / R
- Heat transfer through an assembly: Q = U x A x deltaT
Inputs used
- R-value (hr·ft²·°F/BTU)
- 19
Confidence note: U = 1 ÷ R. The two are exact reciprocals of one another. R-values add across layers; U-values do not. Sum R first, then take the reciprocal once.
What this calculation does not cover
- The conversion trusts the number you type and cannot tell a whole-assembly R from a product label. Insulation, sheathing, cladding, linings, cavities and the interior and exterior surface films all have to be totalled before the reciprocal is taken; a batt's rated R entered on its own returns the U-value of a wall that does not exist.
- Thermal bridging is not in it. Studs, plates, headers, rim joists, cladding fasteners and metal furring carry heat around the insulation, so a framed assembly performs worse than the reciprocal of its clear-field R. That figure comes from a parallel-path or isothermal-planes calculation, not from this one.
- A U-value describes steady-state, one-dimensional conduction and nothing else. Air leakage, wind-washing through loose-fill, convection in unsealed cavities, moisture in the material, thermal mass and solar gain all sit outside it, so a heat loss worked out as U x A x deltaT is the conduction share of the load rather than the whole load.
- R-value is quoted at a rating temperature and does not hold across all service conditions. Foil-faced polyiso in particular delivers less R per inch as the assembly gets cold, and foam boards drift as their blowing agent ages, so the R that applies on a design winter night may not be the one printed on the board.
- This is arithmetic, not a compliance check. Energy codes set maximum U-factors against specifically defined assemblies, and windows and doors are rated as whole units including frame and edge-of-glass, so inverting a glazing R will not answer either question. Everything on this page is imperial: a metric U in W/m2K is roughly 5.68 times the imperial figure shown here.
Add the equipment this sizes
This result is a specification — 0.05263 BTU/hr·ft²·°F — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- Thermal transmittance is the reciprocal of thermal resistance: U = 1 / R
- Heat transfer through an assembly: Q = U x A x deltaT
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
R and U describe the same physical property from opposite ends: resistance to heat flow, and the rate of heat flow itself. Insulation is marketed in R because bigger sounds better, while heat-loss calculations run on U because it multiplies straight through the Q equals U-A-delta-T relationship. The conversion is a pure reciprocal, and the mistake that ruins calculations is doing it too early. Resistances add in series — batt plus sheathing plus cladding plus air films — so the correct order is to total every layer's R and invert once at the end. Summing the individual U-values of each layer produces a number that is not merely imprecise but wrong, typically by a large margin.