The app Angular g-value Calculator allows anyone interested in energy transmission through windows to calculate angular g-values. The user first enters required data such as his geo-coordinates, the number of glass panes, the g-value of the glass and the vertical and the horizontal orientation of the window. When the ‘Calculate’-button is tapped the app calculates the average g-value during the specified summer or winter half-year. If the user enters a specific day and time of the year as well, the average g-value for that day and the exact g-value at that time are calculated.