If the estimate obtained is number, or length, or surface, you would have to obtain the volume and report the volume along with the number, length, or surface. An unbiased method to estimate volume is Cavalieri point-counting.
To avoid confusion, report the number, length, or surface estimate and the volume, do not divide and give the percentage only. This way the reader know what has potentially changed, the number, length, or surface vs. the volume.
This FAQ comes from stereology.info, our curated collection of information and references regarding the use of stereology in the biological sciences. Feel free to review the other FAQs there as well. We hope this thread will spark some in-depth discussion on stereology!