What would be the best way to measure Carbon Dioxide in a Soft Drink can?

And yes, we were going to do it by taste.

Read the nutritional facts which says what percent of CO2 there is. If the serving size is there, the calculate accordingly

I sort of know how carbonated beverages are carbonated: a lot of CO2 CO2 gets pushed into the liquid, and the container is sealed. There are at least two things I don't know. First, how much carbon dioxide is actually dissolved in the liquid? Second, what is the resulitng partial pressure of CO2 CO2 in the headspace and the total pressure in the headspace? I'm interested in cans, plastic bottles, and glass bottles. I know from experience that there is some variation among manufacturers even for the same beverage, so I will be happy with general numbers or a good estimate.