Formula for determining resevoir size?

i'd like to put together a mini ebb and flow system to play and learn with before going full out. my question is, is there a formula for determining what size resevoir would be needed for a specific flood tray size?

https://www.rollitup.org/hydroponics-aeroponics/353164-how-figure-out-resevoir-size.html

Hope this helps you out.

perfect! exactly what i needed. thank you dadio.