U-Value Calculator – Thermal Transmittance
Calculate U-value and R-value for building insulation
Table of Contents
How to Use
- Enter material thickness
- Enter thermal conductivity (λ or k-value)
- Select unit
- Click calculate
What is U-Value?
U-value measures how well a building element conducts heat. Lower U-values indicate better insulation. It's measured in W/m²·K (watts per square meter per degree Kelvin).
Common Material Thermal Conductivity
| Material | λ-value (W/m·K) |
|---|---|
| Mineral wool | 0.035-0.040 |
| Expanded polystyrene (EPS) | 0.030-0.038 |
| Polyurethane foam | 0.022-0.028 |
| Concrete | 1.0-1.7 |
| Brick | 0.6-1.0 |
| Wood | 0.12-0.19 |
Frequently Asked Questions
- What is a good U-value?
- For walls: below 0.3 W/m²·K is good. For roofs: below 0.2 W/m²·K. For windows: below 1.5 W/m²·K. Lower is always better.
- What's the difference between U-value and R-value?
- U-value measures heat transfer (lower is better). R-value measures resistance to heat transfer (higher is better). They are reciprocals: U = 1/R.