If we open our character sheet, it tells us exactly what our Weapon DPS is. But we aren't simply swinging our weapon against our enemies, we rotate through a variety of skills in order to maximize our performance.
Here's a calculator that will give you an approximation of exactly how much damage is doing.
The Calculator is a work in progress and will continue to be updated.
Pretty generalized, and I see what you were going for...but one thing I would recommend you change is to make the damage bonus in cell D12 additive with the skill% bonus in I4 and I5 since for the vast majority of cases this is how self class abilities stack with skill% bonus on gear.