The window dimensions supplied to EnergyPlus are the total opening size (window size including the frame), but deflated by an amount equal to the width of the window frame. The deflation is required because EnergyPlus expects window dimensions excluding the frame whereas DesignBuilder openings include the frame. DesignBuilder takes this approach because it is usually more convenient to enter the size of the opening in the fabric.
The default window areas generated by DB should correspond with the Window to wall % (WWR) setting on the Openings tab , provided you are using either Continuous horizontal or Preferred height facade types.
Tip: switching off frames on the Openings tab causes EnergyPlus windows of the expected dimensions to be generated given the simplistic 'window area divided by total wall area' calculation.