That’s the way I measure with 10 ml syringes. Use some modeling clay to seal off the inlet hole and the throat hole flush with the poppet sealing surface. Measure each half separately . Fill to the top of the male threads. Measure down to the water on the other half the length of the threads. You can seal the end of a syringe with clay then fill it to 6 or so, then drop the inlet check valve and spring into it noting the displacement. The poppet head can be lowered into the syringe and added. Then just subtract the internals from the volume of the empty valve to get the size.1ml =1cc