Grow Room CO₂ Calculator

Calculate exactly how much CO₂ to add per dose, estimate your tank runtime, and see the ppm rise curve for your room. Need help choosing a CO₂ system? Talk to a Grow Expert.

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CO₂ Calculator

Enter your room size and ppm targets. Switch to Advanced to add tank size and dose frequency for runtime estimates.

Room Length (ft) i Interior dimension of your grow space in feet. For tent growers, use the tent's listed footprint.

Room Width (ft) i Interior width of your grow space. Multiply length × width × height to get cubic feet.

Room Height (ft) i Measure floor to ceiling. Standard rooms are 8 ft; warehouse grows may be 10–16 ft.

Ambient CO₂ (ppm) i Outdoor / baseline CO₂ level. Fresh outdoor air is ~400–420 ppm. Use a CO₂ monitor for a precise reading.

Target CO₂ (ppm) i Most growers target 1,200–1,500 ppm during the light cycle. Above 1,500 ppm offers diminishing returns. Never exceed 2,000 ppm.

How to use this calculator

Enter room dimensions — length, width, height in feet. The calculator computes volume automatically.
Set ambient CO₂ — typically 400 ppm for fresh outdoor air. Use a CO₂ monitor for an exact reading.
Set your target ppm — most growers target 1,200–1,500 ppm during the light cycle.
Advanced: select tank size, doses per day, and room seal quality to get a tank runtime estimate.
Tap Calculate — read your CO₂ needed per dose in both ft³ and pounds.

Formula: CO₂ (ft³) = Room Volume (ft³) × (Target ppm − Ambient ppm) ÷ 1,000,000 · Convert to lbs: ft³ ÷ 8.7

Note: Only run CO₂ during the light cycle — plants cannot use CO₂ in the dark.

CO₂ Target Quick Reference — Grow Room ppm by Stage & Method
Growth Stage	Recommended CO₂ (ppm)	Notes	CO₂ Benefit vs Ambient
Propagation / Seedling	400–600 ppm	Ambient or slight enrichment only. Young roots can't support high transpiration.	Minimal
Vegetative	800–1,200 ppm	Start enrichment here. Pair with strong lighting (>400 µmol/m²/s PPFD).	Moderate — ~15–25% faster growth
Flowering (early)	1,200–1,500 ppm	Peak benefit window. Requires dialed-in VPD and adequate light intensity.	High — up to 30% yield increase
Flowering (late)	800–1,000 ppm	Some growers taper CO₂ in the final 2 weeks. Less consensus here.	Moderate
Ambient (no enrichment)	~400 ppm	Outdoor air baseline. Still supports growth but limits photosynthetic rate.	Baseline
Maximum safe level	≤ 2,000 ppm	Above 2,000 ppm can cause stomatal closure and stress. OSHA limit for workers is 5,000 ppm.	Diminishing returns above 1,500

📈 CO₂ Rise Curve — ppm Over Dosing Window Area Chart ▾

CO₂ level during dosing

Target ppm

Ambient level

Calculate above to see your CO₂ rise curve. The chart shows ppm building from ambient to target across your dosing window, then decaying between doses.

☁️ Run the calculator above to generate your ppm rise curve.

Frequently Asked Questions

What CO₂ level should I target in my grow room?

Most growers target 1,200–1,500 ppm during the light cycle for maximum photosynthetic efficiency. Ambient outdoor air is ~400 ppm. Above 1,500 ppm offers diminishing returns for most cultivars, and above 2,000 ppm can stress plants by triggering stomatal closure. Pair elevated CO₂ with adequate light intensity — CO₂ enrichment has little effect if your PPFD is below 600 µmol/m²/s.

How do I calculate how much CO₂ to add?

The formula is: CO₂ volume (ft³) = room volume (ft³) × (target ppm − ambient ppm) ÷ 1,000,000. Convert to pounds by dividing by 8.7 (the volume of one pound of CO₂ gas at room temperature). This gives you how much CO₂ is needed to raise the room from ambient to target in a single dose — assuming a perfectly sealed room.

How often should I dose CO₂?

CO₂ should only run during the light cycle — plants only use CO₂ during photosynthesis. Most growers dose every 15–60 minutes via a controller with a CO₂ monitor at canopy level. Dosing frequency depends on room seal quality, plant transpiration rate, and your exchange rate (air leakage). A well-sealed room may need doses every 30–60 minutes; a leaky room may need more frequent, shorter doses.

How long will a CO₂ tank last?

Tank longevity depends on tank size (lbs of CO₂), room volume, target ppm, and doses per day. A 20 lb tank in a 10×10×8 ft room targeting 1,200 ppm with 12 doses/day might last roughly 10–18 days under good seal conditions. Use the Advanced mode in this calculator to enter your tank size and dose frequency for a runtime estimate. Always keep a spare tank on hand.

Should I use a CO₂ tank or a CO₂ burner/generator?

Tanks (compressed CO₂) are precise, clean, and generate no heat or moisture — ideal for sealed rooms and small to medium grows. Burners/generators produce CO₂ by combustion, which also adds heat and water vapor — better suited for large rooms with robust HVAC. This calculator applies to both: calculate the lbs/dose needed and apply to whichever source you use.

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