Dehumidifier ratings are in pints per day, and the mistake most growers make is sizing to the room like a basement unit. Plants add water to the air constantly, so the right number comes from transpiration, not square footage.
The quick estimate
Plants transpire roughly what you feed them. If a room takes 40 gallons of water a day, expect most of that to end up in the air, which is about 320 pints. That is your daily dehumidification load before you account for the HVAC pulling some of it out.
Rating conditions matter
Commercial dehumidifiers are rated at 80 F and 60 percent humidity. Residential units are rated at higher humidity and remove far less at the conditions a grow room runs. Compare units on the same rating conditions, or use the manufacturer's performance curve at your target setpoint.
Placement and drainage
Hang or mount units so airflow crosses the canopy, and plumb a drain line. A 180 pint unit produces more than 20 gallons a day; a bucket is not a plan.
Every dehumidifier we sell lists its rating conditions on the product page. If yours does not say, ask before you buy.