Are you trying to automate it? You have to look at the cells and make a decision, is it a sphere, a prolate or oblate spheroid, a cone. Then measure the cell and calculate the volume based on the assumed 3D shape. If your software can ID the cell (like the flow-cam software) it may be able to do this for you after you teach it what is what...
Hi Donald, thank you very much for your reply. This is indeed what I usually do, but I have read of computational algorithms that can handle any shape without prior decision and appear quite precise. What I actually would like to know is if commercial software employ such kind of algorithms or they ID the cell and then "choose" the proper equation or, again, simply assume any cell is a prolate spheroid.