Measuring CO2 I have been searching for an answer to this for quite a while, so I'm hoping somebody here can help me out. I've spent quite a bit of time digging and reading, and I've found plenty of information, but I'm not always sure what to make of it. I am working on making myself a small electronic device to measure the dissolved CO2 in water in ppm by weight. I'm going to make a small sealed chamber that will have an opening only to the water (but not to the atmosphere). The CO2 will off gas into the chamber until the concentration of CO2 in chamber becomes at equilibrium with the concentration in the water. I know that some of the CO2 will be converted into carbonic acid, but as I understand it, the majority of it will remain as CO2, and for the precision I'm going for I think I can just ignore that. I'm going to place a small CO2 air sensor in the chamber that I will connect to a micro controller. The CO2 sensor reads concentration in ppmv. I'll also put a temperature sensor in there since I'm pretty sure I'll need to correct for temperature. The problem I'm having is taking the ppm by volume and equating it to the concentration of CO2 in water, which needs to be reported in ppm by weight. I can't find a formula to do the conversion, and it's been so long since I took physics (I'm 37), so I'm completely unable to figure this out at this point. Basically, I'm trying to figure out if it's V ppmv in the chamber, than what's the W ppmw in the water. Anybody have any ideas on how you'd calculate this?