How can we calculate the volume solid in a paint, from WFT or coverage of the paint film?

Do you mean the volume of paint on your wall? If so, multiply the thickness you obtained in your previous post by the area that the paint covered.

What do you mean by WFT?

See here:

https://www.askmehelpdesk.com/physics/calculation-wft-355233.html

It stands for Paint Wet Film Thickness according to the OP.

Thanks, won't that thickness change dramatically as the paint dries?

Well.. who knows? :(

OK, I can calculate the volme of the paint in the can but not the solids in the paint unless the manufacturer provides specifics about how much solvent/carrier is there compared to the pigments. I can't answer this question as it is stated and wonder if anyone can.