Free calculator
Grow tent fan size calculator
Results update as you type. The page URL keeps your inputs, so you can bookmark or share them.
How this works
Base CFM = tent volume ÷ exchange minutes. Losses: carbon filter +25%, flexible duct +5% per 5 ft, each 90° bend +10%. Heat check: CFM ≥ watts × 3.412 ÷ (1.08 × ΔT°F). We take the larger of the two and add headroom. Fan class: ≤190 CFM → 4″, ≤400 → 6″, ≤750 → 8″, ≤1,200 → 10″.
Then compare fans in our best inline fan for a grow tent guide.
FAQ
What size inline fan do I need for a 4x4 grow tent?
A 4×4×6.7 ft tent is about 107 ft³. With one air exchange per minute, a carbon filter, 8 ft of duct, one bend and 25% headroom you need roughly 200 CFM, so a 6-inch fan run on a speed controller is the usual choice.
How much does a carbon filter reduce airflow?
Plan on about 25% more fan capacity with a carbon filter. Each 90° bend adds roughly 10% and every 5 ft of flexible duct about 5%.
Should I oversize my exhaust fan?
Yes, modestly. A fan running at 60–70% on a controller is quieter and has headroom for hot days.