R-Value ↔ U-Value Converter
Convert between R and U in both SI and US unit systems — without the 5.68× trap.
US 'R-19' insulation is RSI 3.3, U = 0.30 W/m²K. Mixing systems is the most common spec-sheet blunder in international projects.
Formula
R-Value ↔ U-Value Converter is a free r value to u value for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About R-Value ↔ U-Value Converter
Convert between R and U in both SI and US unit systems — without the 5.68× trap. The calculation implements U = 1/R; R_US = 5.678 × R_SI (ASHRAE Fundamentals, ch. 25–27). US 'R-19' insulation is RSI 3.3, U = 0.30 W/m²K. Mixing systems is the most common spec-sheet blunder in international projects.
How to use R-Value ↔ U-Value Converter
- 1Enter R-value (SI) in m²K/W.
- 2Read U-value (SI), R-value (US), U-value (US) instantly — no submit button needed.
Why use R-Value ↔ U-Value Converter?
- ✓Implements the standard formula — U = 1/R; R_US = 5.678 × R_SI
- ✓Reference cited on-page: ASHRAE Fundamentals, ch. 25–27
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the R-Value ↔ U-Value Converter use?+
It computes U = 1/R; R_US = 5.678 × R_SI, per ASHRAE Fundamentals, ch. 25–27. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
US 'R-19' insulation is RSI 3.3, U = 0.30 W/m²K. Mixing systems is the most common spec-sheet blunder in international projects.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the R-Value ↔ U-Value Converter free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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