Insulation R-Value Converter
Convert between R-value (imperial) and RSI (metric) insulation ratings.
Includes common material thicknesses and their R-values.
Type in any field — the others update instantly.
The R-value measures thermal resistance — how well a material resists heat flow through it. A higher R-value means better insulation and less heat loss.
Conversion between imperial and metric:
- 1 R-value (ft2 F h/BTU) = 0.176110 RSI (m2 K/W)
- 1 RSI (m2 K/W) = 5.678263 R-value
The formulas are simply:
- RSI = R-value x 0.176110
- R-value = RSI x 5.678263
Common insulation materials and their R-values per inch (per 25.4 mm):
| Material | R per inch | RSI per 25.4mm |
|---|---|---|
| Fiberglass batts | 3.1-3.4 | 0.55-0.60 |
| Cellulose (blown) | 3.2-3.8 | 0.56-0.67 |
| Mineral wool batts | 3.0-3.3 | 0.53-0.58 |
| Spray foam (open cell) | 3.6-3.8 | 0.63-0.67 |
| Spray foam (closed cell) | 6.0-7.0 | 1.06-1.23 |
| Rigid XPS foam board | 5.0 | 0.88 |
| Rigid polyiso foam board | 5.6-6.5 | 0.99-1.14 |
| EPS (expanded polystyrene) | 3.6-4.2 | 0.63-0.74 |
Recommended total R-values by climate zone (USA):
| Climate Zone | Attic | Walls | Floor |
|---|---|---|---|
| Zone 1 (hot/tropical) | R-30 | R-13 | R-13 |
| Zone 3 (warm) | R-38 | R-13 | R-19 |
| Zone 5 (moderate) | R-49 | R-20 | R-25 |
| Zone 7 (cold) | R-60 | R-21 | R-30 |
Practical tips:
- R-values are additive: two layers of R-13 insulation stacked together give R-26 total.
- The R-value per inch varies by material, so thickness alone does not determine insulation performance.
- In metric countries like Canada, Europe, and Australia, RSI is the standard unit used in building codes.
- Gaps, compression, and moisture all reduce the effective R-value significantly, so proper installation is as important as the material rating itself.