Greenhouse CO2 Requirement Calculator
Estimate the volume of CO₂ gas needed to raise greenhouse air concentration to a target level based on the structure's volume. Ideal for commercial growers scheduling CO₂ injection sessions to maximize photosynthesis rates.
About this calculator
Plants in a sealed or semi-sealed greenhouse can quickly deplete ambient CO₂ (normally ~400 ppm) on sunny days, limiting photosynthesis. Supplementing CO₂ to 800–1,200 ppm can boost crop yields by 20–30%. The volume of CO₂ gas needed is proportional to the greenhouse air volume and the desired concentration increase. The formula is: CO₂ Required (cu ft) = (greenhouse_volume × target_CO₂_increase) / 1,000,000. The divisor of 1,000,000 converts the parts-per-million concentration into a volume fraction. This result gives you cubic feet of pure CO₂ gas at ambient pressure; converting to pounds requires multiplying by the density of CO₂ (~0.1144 lbs/cu ft at 68°F). Because greenhouses are not perfectly sealed, growers must account for ventilation losses and run injections in short, frequent cycles during daylight hours.
How to use
Your greenhouse is 100 ft long, 30 ft wide, and 12 ft tall, giving a volume of 36,000 cu ft. You want to raise CO₂ from ambient 400 ppm to 1,000 ppm — a target increase of 600 ppm. Step 1 — Apply the formula: (36,000 × 600) / 1,000,000 = 21,600,000 / 1,000,000 = 21.6 cu ft of CO₂ gas. Step 2 — Convert to weight: 21.6 × 0.1144 ≈ 2.47 lbs of CO₂ per injection cycle. Knowing this helps you size your CO₂ cylinder or generator and plan refill schedules.
Frequently asked questions
What is the optimal CO2 concentration level for greenhouse crop production?
Most greenhouse vegetable and flower crops respond best to CO₂ concentrations between 800 and 1,200 ppm, roughly two to three times the ambient outdoor level of ~400 ppm. Tomatoes, cucumbers, and lettuce show significant yield and quality improvements in this range. Concentrations above 1,500 ppm offer diminishing returns for most crops and can cause stomatal closure in some species. The ideal target depends on light intensity — higher CO₂ is only beneficial when photosynthetically active radiation (PAR) is also high.
How do I convert greenhouse CO2 volume requirements into pounds or kilograms for ordering gas?
Once you calculate the required volume of CO₂ in cubic feet, multiply by the density of CO₂ gas at room temperature, which is approximately 0.1144 lbs per cubic foot (or 1.832 kg/m³ in metric units). For example, 21.6 cu ft × 0.1144 = 2.47 lbs of CO₂. Commercial CO₂ is sold by weight, typically in 50 lb cylinders or by bulk tank delivery for larger operations. Dividing your total daily CO₂ need by cylinder size tells you how many cylinders to keep on hand.
When should I inject CO2 into my greenhouse for maximum plant benefit?
CO₂ injection is only beneficial during daylight hours when plants are actively photosynthesizing. The best window is typically from sunrise to about two hours before sunset. During periods of high ventilation — hot summer days when vents are fully open — CO₂ enrichment is largely wasted because the gas escapes before plants can use it. Focus injection on cool, bright mornings with vents partially or fully closed, and use a controller linked to a CO₂ sensor to maintain target concentration automatically.