How should I best estimate initial dissolved Co2?

I'm ready to cap the next batch and was looking at prime sugar requirements. I can do the math and figure it all out .. but the weak point is the starting asumption. I only have a very rough estimate on the current beer condition. I have reached final stable gravity (fairly dry at 1.0023 ).
So my question is, can I just assume I'm running ~ 0.5 volumes at RT(22C) and 1/4" of air lock pressure? Anybody now a better way to get a first best estimate on dissolved Co2?

I suppose I could draw a sample off and boil out the gas and do a mass-loss analysis .. but that sounds like work and error in the making just to reinvent the wheel.

What do you all use as a guide for your starting point estimate?

Thanks,
Kirk

 

Thanks VikeMan. I've seen a few of those and some give variable answers. the one you gave looks good enough.
I ended up finding a formula online that takes into account; altitude, temp , beer density, and alc content. Similar bottom line but now I'm ready for anything ...so I'll run with it. Not really all that critical I suppose when your estimating finals in 1/10ths.