Free calculator

Dehumidifier sizing calculator

Water in equals water out: nearly every liter you feed a grow room comes back as vapor, and everything a drying harvest loses ends up in the air. Match removal capacity to that load or RH drifts up every day.

Moisture load

Water fed per daygal/dayTotal irrigation across all plants, minus what goes to drain.Fraction transpired%What isn't retained in biomass or drained returns to the air. 90% is typical at steady state.

Result

Includes a 1.3× real-world safety factor

Rated capacity to shop for

47pints/day

= 22.1 L/day

Actual moisture load

36.0pints/day

17.0 L/day before the safety factor

Pint ratings (AHAM) are measured at 80 °F / 60% RH — in a cooler room or at a lower RH setpoint the same unit removes much less, which is what the 1.3× factor covers. If your AC runs constantly it also removes water; this sizing treats the dehumidifier as doing all the work.

Not sure what RH you should hold? Find your VPD target →