Use the result as a scenario, not a black box
Start with the amount of water you expect the room to return to the air each day, then add a design margin. This avoids pretending that plant count alone can determine dehumidifier size. The calculator converts your moisture estimate into pints per day and liters per day and shows a recommended rated capacity.
Dehumidifiers are rated by how much water they can remove in a day under defined test conditions. This calculator begins with a moisture-load estimate you control. That is more transparent than a black-box plant-count formula because irrigation style, runoff, room temperature, stage of growth and HVAC behavior can all change how much moisture ends up in the air.
How the math works
One US gallon equals 8 pints and approximately 3.785 liters. Base pints/day = gallons/day × 8. Recommended rated capacity = base pints/day × (1 + safety factor). Capacity per unit = recommended capacity ÷ unit count.
A room that needs to remove 12 gallons of water per day has a base load of 96 pints/day. With a 25% design margin, the planning target becomes 120 pints/day. Two equal units would each need about 60 pints/day of rated capacity.