Here’s a simplified formula to give you an idea of how the Uw value is calculated:

Where:

- Uw is the overall U-value of the window.
- Ag is the area of the glazing (glass).
- Ug is the U-value of the glazing.
- Af is the area of the frame.
- Uf is the U-value of the frame.
- Lg is the length of the glass edge.
- Ψg (Psi value) is the linear thermal transmittance of the glass edge.

For example, if you have a window with:

- A glass area (Ag) of 1.2 m² with a Ug value of 1.1 W/(m²K),
- A frame area (Af) of 0.3 m² with a Uf value of 1.5 W/(m²K),
- A glass edge length (Lg) of 6 m with a Psi value (Ψg) of 0.04 W/(mK),

The overall U-value (Uw) for the window, calculated using the given formula, is approximately Uw=1.34 W/(m²K).

This value represents the heat transfer coefficient of the entire window, including the frame and the glazing.

This example is a simplification and does not take into account all the possible complexities of a real-world scenario, but it illustrates the general approach to calculating the overall U-value of a window.