If you are bouncing your flash, all your guide number calculations will need to be changed.
You will need to include both of the following in your calculations:
1) the total distance of the entire light path (flash to bounce surface to subject); and
2) the light loss caused by incomplete reflection by the bounce surface.
Guide numbers don't work well with bounced flash, unless you use a standard bounce reflector in a standard configuration, with a re-calibrated guide number.