You need to find a formula for the calculation or you can do what I did and waste time and money and buy several small ones over time that wont do the job and in the end step up and spend the cash or get real creative.

I found this on line, "When spread in a day's span, your grow room will need 5 pints of water an hour. A pint is equal to a pound of moisture, so a room with 20 plants needs 5 pounds of moisture an hour. Dehumidifier sizes are usually ranging from 30 up to 300 pints. The bigger the size is, of course, the more expensive it'll be."

Grow weed easy.com may have some solid suggestions too

This page has the formula I use

https://hydrobuilder.com/learn/size-dehumidifier-indoor-garden/