Recent Calculation History
Formula Used
RSI equals R divided by 5.678263. R equals RSI multiplied by 5.678263. U-values equal one divided by thermal resistance.
RSI = R ÷ 5.678263 R = RSI × 5.678263 Metric U-value = 1 ÷ RSI Imperial U-factor = 1 ÷ R
How to Use
Select the conversion direction first. Enter one resistance value and choose precision. Submit the form to view detailed results.
Add layers for a complete assembly. Enter film values only when appropriate. Use project data for thermal bridging estimates.
Use thickness tools for material planning. Compare alternatives before choosing an insulation product. Export results for records, reports, or discussions.
Worked Example
Assume the insulation rating is R-30. Divide thirty by the conversion factor. The result is approximately RSI 5.283.
RSI = 30 ÷ 5.678263 RSI = 5.2833 m²·K/W R-30 ≈ RSI-5.28
| R-value | RSI value |
|---|---|
| R-5 | 0.881 |
| R-10 | 1.761 |
| R-13 | 2.289 |
| R-19 | 3.346 |
| R-20 | 3.522 |
| R-21 | 3.698 |
| R-30 | 5.283 |
| R-38 | 6.692 |
| R-49 | 8.629 |
| R-60 | 10.567 |
R, RSI, and U-Value Guidance
R-value uses Imperial thermal resistance units. RSI uses metric thermal resistance units. Higher resistance usually means slower heat transfer.
U-value measures heat transfer instead. Lower U-values generally indicate stronger insulation performance. Zero resistance makes reciprocal calculations undefined.
Labelled insulation values may exclude framing. Air gaps and installation quality also matter. Verify final assemblies using applicable building requirements.
Frequently Asked Questions
1. What does an R-value measure?
R-value measures resistance to heat flow in Imperial units. Higher values usually indicate better insulating performance. Assemblies may perform differently because framing creates thermal bridges.
2. What does RSI mean?
RSI expresses thermal resistance using metric units. It uses square metres kelvin per watt. Higher RSI values indicate greater resistance against heat flow.
3. How do I convert R to RSI?
Divide the R-value by 5.678263. Keep extra decimals during intermediate calculations. Round only the final value for clearer reporting.
4. How do I convert RSI to R?
Multiply the RSI value by 5.678263. The result uses Imperial resistance units. Maintain consistent units throughout every project calculation step.
5. What is a U-value?
U-value measures heat transfer through an assembly. It is the reciprocal of resistance. Lower U-values normally represent better overall thermal performance.
6. Can I add insulation layer values?
Yes, series layer resistances can be added. Convert mixed units before combining them. Thermal bridges may reduce actual whole-assembly resistance significantly.
7. Are air-film values always included?
No, air-film values depend on conditions. Orientation and airflow can change them. Use values required by your chosen calculation method.
8. Does thickness determine insulation resistance?
Thickness affects resistance when material performance remains consistent. Use the manufacturer’s rated resistance rate. Compression and moisture may change actual installed performance.
9. Can this replace professional energy modelling?
No, this calculator provides planning estimates. Complex assemblies require detailed thermal modelling. Confirm regulated projects with qualified building professionals before construction.