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Calculation Machine

Grow Tent CFM Calculator

Inline fan size for a grow tent with filter losses.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Fan size to buy
190 CFM
Base tent volume
104 cu ft (one exchange per minute)
Total uplift applied
65%
Suggested duct
4 in
Passive intake area
57 sq in minimum

Working

  1. 1104 cu ft x 1.65 = 172 CFM

Quick answer

A grow tent should exchange its full air volume every one to three minutes, then add allowances for the carbon filter, ducting and light heat.

The formula

CFM = tent volume x (1 + filter% + duct% + heat%)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Tent length4 ft
  • Tent width4 ft
  • Tent height6.5 ft
  • Carbon filterYes
  • Light wattage600 W
  • Number of duct bends2

Result

  • Fan size to buy190 CFM
  • Base tent volume104 cu ft (one exchange per minute)
  • Total uplift applied65%
  • Suggested duct4 in
  • Passive intake area57 sq in minimum

How to use the Grow Tent CFM Calculator

  1. 1Enter your tent's footprint and height in feet.
  2. 2Say whether you run a carbon filter and how many bends the ducting has.
  3. 3Add the light wattage so heat removal is included, then buy the next fan size up with a speed controller.

Frequently asked questions

What size fan for a 4x4 tent?

Around 200–260 CFM with a carbon filter and 600 W of light — a 6 inch inline fan is the usual choice.

Should the fan run constantly?

Yes during lights-on; many growers drop to a lower speed at night to hold humidity.

About this calculator