R-value ↔ RSI Converter
R-value to RSI and back, with climate-zone recommended minimums.
How to use
Type a value in either field; the other updates live. Higher numbers mean more thermal resistance.
- Enter R-value (imperial, in ft²·°F·h/BTU) to get its RSI.
- Or enter RSI (metric, m²·K/W) to get the equivalent R-value.
- Check the reference table for the minimum value required in your climate zone.
- Actual code-required insulation depends on the National Building Code, ASHRAE 90.1, and your local jurisdiction.
Reviewed 3 June 2026 · methodology cited
About this converter
R-value and RSI both measure thermal resistance — the resistance a building assembly presents to the flow of heat. R-value uses imperial units (ft²·°F·h/BTU); RSI uses metric (m²·K/W). They describe the same physical property; only the unit system differs.
This converter handles the bidirectional math and lists the minimum effective R and RSI values required by the National Building Code (NBC) Section 9.36 by Canadian climate zone. These are minimum prescriptive values — actual code-approved walls, attics, and basements may use higher values, alternative compliance paths, or performance-based modelling.
The conversion factor
The conversion is a simple multiplicative factor: RSI = R-value × 0.1761. Going the other way: R-value = RSI × 5.678. The factor 5.678 comes from the units: 1 ft²·°F·h/BTU = 5.678 26 × 10⁻¹ m²·K/W exactly.
A worked example: R-20 batt insulation (typical 2×6 wall stud cavity in older construction) = 20 × 0.1761 = RSI 3.5. R-60 attic insulation (modern code minimum for many cold-climate zones) = 60 × 0.1761 = RSI 10.6. R-12 basement-wall insulation (NBC 9.36 effective value for unheated slab edges in zone 5) = 12 × 0.1761 = RSI 2.1.
Note the distinction between nominal R-value (the rating of an insulation product on its own) and effective R-value (the value of the entire assembly including framing, sheathing, drywall, and air films). Code values are effective values. A 2×6 wall with R-22 batts and minimal exterior continuous insulation has an effective value closer to R-17 because of thermal bridging through the studs. The reference table below shows effective values.
Canadian climate-zone insulation minimums (NBC 9.36)
| Zone | Climate | Wall R / RSI | Attic R / RSI | Basement R / RSI |
|---|---|---|---|---|
| 4 | < 3000 | R-22 / RSI 3.85 | R-50 / RSI 8.81 | R-12 / RSI 2.10 |
| 5 | 3000–3999 | R-24 / RSI 4.23 | R-50 / RSI 8.81 | R-17 / RSI 2.99 |
| 6 | 4000–4999 | R-24 / RSI 4.23 | R-60 / RSI 10.57 | R-17 / RSI 2.99 |
| 7A | 5000–5999 | R-29 / RSI 5.11 | R-60 / RSI 10.57 | R-17 / RSI 2.99 |
| 7B | 6000–6999 | R-29 / RSI 5.11 | R-60 / RSI 10.57 | R-17 / RSI 2.99 |
| 8 | ≥ 7000 | R-31 / RSI 5.46 | R-60 / RSI 10.57 | R-22 / RSI 3.85 |
Insulation notes
Insulation goes everywhere heat wants to escape: walls, attic, basement, rim joists, slab edges. The biggest gains usually come from where there is the least insulation today — adding R-20 to a previously uninsulated attic saves more energy than upgrading an R-40 attic to R-60. Air sealing — finding and closing leaks — typically pays back faster than additional insulation alone.
Be aware of moisture risk. Adding exterior insulation to a wall changes the dew point inside the wall assembly. Done correctly it keeps the sheathing warmer and dryer; done wrong it traps moisture inside. The 1/3-2/3 rule (one-third of the thermal resistance outside the structural sheathing, two-thirds inside) is a common starting point but the actual ratio depends on climate. Anything more than R-5 of exterior continuous insulation in cold climates needs a careful look at vapour control. This is reference math, not a wall-assembly design tool — the design belongs to a building scientist or qualified envelope contractor.
Frequently asked questions
What is the difference between R-value and RSI?
They measure the same thing in different unit systems. R-value uses imperial units (ft²·°F·h/BTU); RSI uses metric (m²·K/W). RSI = R × 0.1761 exactly. Canadian building documents often list both; US documents list R only.
What is "effective R-value"?
It is the R-value of an entire assembly — insulation, framing, sheathing, drywall, air films — averaged over the area. Building codes specify effective R because that is what actually limits heat loss. The insulation alone is "nominal R"; framing reduces the assembly value through thermal bridging.
What climate zone am I in?
Canadian climate zones are based on heating degree days (HDD): Zone 4 = < 3000 HDD (Vancouver), Zone 5 = 3000–3999 (Toronto, Montreal), Zone 6 = 4000–4999 (Ottawa, Calgary), Zone 7A = 5000–5999 (Edmonton, Saskatoon), Zone 7B = 6000–6999 (Winnipeg, Quebec north), Zone 8 = ≥ 7000 (Yellowknife). Your local building department will confirm the exact zone for your municipality.
How much insulation should I add?
For new construction: meet or exceed the code minimum for your climate zone. For retrofits: an energy audit (typically a blower-door test and infrared scan) identifies the highest-payback improvements. Adding R-30 to a previously R-20 attic is usually cheaper and more impactful than adding R-15 to a previously R-40 attic.
Does this calculator account for thermal bridging?
No. It is a unit converter between R and RSI. Thermal-bridging calculations belong in a wall-assembly worksheet — typically a 2D heat-flow analysis or the parallel-path method described in ASHRAE Fundamentals. The reference table values are pre-calculated effective R, but only for the specific assemblies the code committee studied.
Where do the NBC 9.36 values come from?
NBC Section 9.36 is the energy efficiency section of the Canadian National Building Code, first published as a separate part in NBC 2010 and significantly tightened in NBC 2020. Section 9.36.2 lists prescriptive minimum effective R / RSI values by climate zone for opaque assemblies. The full document is published by the National Research Council Canada (NRC); local provincial codes adopt and modify it.