Grow Tent CFM Calculator
Inline fan size for a grow tent with filter losses.
Enter your values
Enter the tent length in ft.
Enter the tent width in ft.
Enter the tent height in ft.
Choose one of: Yes, No.
Enter the light wattage in W.
Enter the number of duct bends you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
- 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.
CFM = tent volume x (1 + filter% + duct% + heat%)
At a glance
| What it does | Inline fan size for a grow tent with filter losses. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Tent length, Tent width, Tent height, Carbon filter, Light wattage, Number of duct bends |
| Main output | Fan size to buy |
| Formula | CFM = tent volume x (1 + filter% + duct% + heat%) |
| Cost | Free — no sign-up, no download |
How to use the Grow Tent CFM Calculator
- 1Enter your tent's footprint and height in feet.
- 2Say whether you run a carbon filter and how many bends the ducting has.
- 3Add the light wattage so heat removal is included, then buy the next fan size up with a speed controller.
Inputs explained
- Tent length(ft)
- Enter the tent length in ft.
- Tent width(ft)
- Enter the tent width in ft.
- Tent height(ft)
- Enter the tent height in ft.
- Carbon filter
- Choose one of: Yes, No.
- Light wattage(W)
- Enter the light wattage in W.
- Number of duct bends
- Enter the number of duct bends you are working with.
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
Results
- 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
- 104 cu ft x 1.65 = 172 CFM
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.
What do I need to enter into the Grow Tent CFM Calculator?
Just 6 values: tent length, tent width, tent height, carbon filter, light wattage, number of duct bends. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Grow Tent CFM Calculator work out the 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. It applies the formula CFM = tent volume x (1 + filter% + duct% + heat%) and shows the working so you can check each step by hand.
Is the Grow Tent CFM Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.