Grow Room CO₂ Calculator

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.

Shop CO₂ Devices Read the Full Guide

CO₂ Calculator

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

How to use this calculator
  1. Enter room dimensions — length, width, height in feet. The calculator computes volume automatically.
  2. Set ambient CO₂ — typically 400 ppm for fresh outdoor air. Use a CO₂ monitor for an exact reading.
  3. Set your target ppm — most growers target 1,200–1,500 ppm during the light cycle.
  4. Advanced: select tank size, doses per day, and room seal quality to get a tank runtime estimate.
  5. 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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