Hi guys and gals. Hobbyist, not a student. I've had great input here in the past. Thank you in advance for any direction and help figuring this out. -Seth- 1. The problem statement, all variables and given/known data I'd like to learn how to calculate relative humidity, saturation, and dew point under differing pressures and temperatures. All the information I've been able to find on-line seems to ignore one or the other and assumes a constant condition for the ignored value. Maybe there is a good reason for this? Anyway, my inquisition is turbo charged engine related. I'd like to learn to calculate: For given atmospheric conditions of, let's say, Sea Level, 59ºF, 90%RH If this air were compressed to 29.4psia (14.7psig) and after compression the air was 221ºF, what would it's resulting relative humidity be, whats the saturation point, and what's the dew point? If the compressed air (above), 29.4psia & 221ºF, is cooled to 84ºF, what would it's resulting relative humidity be, whats the saturation point, and what's the dew point? What if the pressure were lowered slightly too, to say... 28psia and 84ºF? 2. Relevant equations This is my biggest problem. I'm looking high and low for an equation and can't seem to find one that does what I want. I want to input pressure and temperature and have the solution indicate how much water air can hold under those conditions. Any direction at all is greatly appreciated. 3. The attempt at a solution I have no idea where to start. I'm almost wondering if pressure doesn't have anything to do with it. But it must. Mustn't it? If this inquiry is better suited in a different section, by all means move it please. Any links to something that might explain this or just an equation I can try out is greatly appreciated. Or, if you can kind of explain in layman's terms the relationship and effects temperature and pressure have on how much water air can hold.