Convert an SI R-value into U-value and estimate heat flow through an area at a given temperature difference.
| U (W/m²·K) | – |
| Heat flow (W) | – |
Use this calculator when a product lists R in m²·K/W and you want U and a watts figure. Enter R, the area, and ΔT.
U = 1 / R. Watts = U × area × ΔT. Area can be entered in square metres (m²) or square feet (ft²). R stays in m²·K/W (SI). ΔT stays in K.
This is a single layer. It does not add air films, thermal bridges, or a U.S. imperial R-value (those are about 5.678 times larger).
R (m²·K/W): SI thermal resistance.
Area: Element area, in m² or ft².
ΔT (K): Indoor minus outdoor, in kelvin.
U (W/m²·K): Thermal transmittance.
Heat flow (W): Steady heat flow in watts.
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