About Refrigeration

http://www.simetric.co.uk/

I believe you might be looking to find out the amount of refrigerant in the system vs. the cooling capacity needed.

There isn't a direct correlation between tons of refrigeration and volume, because volume changes in a system regardless of small or large cooling capacity(which is what "tons of refrigeration" refers to).

Volume variation directly relate to; temperature change, and change of state.

For the psychrometric properties of air, other factors such us humidity content also affect volume directly.

As far as pounds of refrigerant(MASS, not volume), per Tons of Refrigeration(cooling capacity). They obviously are proportional to each other(the more capacity, the more refrigerant you'll need); however it is not wise to exclude other factors such: heat transfer surface area and physical properties of the material it is built with(Al, Cu,...), temperature difference, design temperature, compressor type, pipe sizes and velocity, refrigerant characteristics.

k*Q_g*ρ_g/h_fg, where k is a constant to match the units of choice.