CO2 Grow Room Calculator
Work out how much carbon dioxide a grow room needs to reach a target ppm, how long the injection takes and what it costs per hour to hold.
🌱 What is CO2 Grow Room Enrichment?
CO2 grow room enrichment is the practice of deliberately raising the carbon dioxide concentration in a sealed growing space above the outdoor background level, which currently sits near 420 parts per million. Carbon dioxide is one of the two raw materials of photosynthesis, and in a bright, well-watered, well-fed room it is very often the first thing to run short. Lifting the concentration to somewhere between 800 and 1,200 ppm can raise photosynthetic rate substantially, which shows up as faster growth, heavier fruit set and a shorter time to harvest. The trade is that the gas costs money, must be delivered accurately, and is dangerous to people at high concentrations.
The sums come up in several different situations. A grower fitting a tank and regulator to a small tent needs to know whether a 10 litre per minute flow will fill the space in one minute or twenty. A greenhouse manager pricing a season of enrichment needs the continuous hold rate, not the one-off fill, because that is where nearly all the gas goes. A room designer weighing extra sealing against extra gas needs to see how the hourly consumption scales with air changes per hour. Someone sizing a tank wants the mass, in kilograms or pounds, that a week of operation will consume.
The most useful thing to understand is that a room never simply fills up and stays full. Air exchange, whether from an extraction fan, a door opening, or plain leakage through the fabric, continuously dilutes enriched air back towards ambient. The result is an exponential approach to a ceiling concentration set by the ratio of injection flow to leak rate, not a straight climb to whatever number you choose. If that ceiling sits below your target, no amount of injection time will get you there, and the fix is to seal the room or raise the flow rate rather than to run the regulator longer. This calculator models that behaviour directly, which is why it asks for air changes per hour.
A second point worth stating plainly is that parts per million is a volume ratio, so the gas volume needed is beautifully simple: room volume times the ppm lift times one millionth, with the units cancelling out. Temperature does not change that volume at all. It changes only the mass, because warm gas is less dense, and the calculator applies the ideal gas law at your room temperature to convert litres into grams or cubic feet into ounces. That is the number that matters when you are working out how many days a cylinder will last.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Small Sealed Tent Room
3 m by 3 m by 2.5 m, target 1,200 ppm, 10 L/min regulator, 0.5 air changes per hour, 24 °C
Example 2 — Leaky Commercial Room
6 m by 4 m by 3 m, target 1,500 ppm from 400 ambient, 15 L/min, 1.0 air change per hour, 26 °C
Example 3 — Imperial 10 by 10 Room
10 ft by 10 ft by 8 ft, target 1,200 ppm, 20 ft³/hr regulator, 0.5 air changes per hour, 75 °F
Example 4 — Perfectly Sealed Cabinet
2 m by 2 m by 2.2 m, target 1,000 ppm from 400 ambient, 5 L/min, zero air changes, 22 °C
❓ Frequently Asked Questions
🔗 Related Calculators
How much CO2 does a grow room need to reach 1200 ppm?
Multiply the room volume by the ppm lift and by one millionth. A 22.5 cubic metre room going from 420 to 1,200 ppm needs 22.5 times 780 times 0.000001, which is 0.01755 cubic metres, or 17.55 litres of gas. At 24 degrees Celsius that gas weighs about 31.7 grams.
What is the formula for CO2 enrichment in a grow room?
CO2 volume = room volume times (target ppm minus ambient ppm) times 10 to the power minus 6. Parts per million is a volume ratio, so the units cancel: cubic metres in gives cubic metres of gas, cubic feet in gives cubic feet of gas. Multiply by gas density for the mass.
What CO2 ppm is best for plants?
Most crops respond well between 800 and 1,200 ppm, and gains flatten out by about 1,500 ppm. Above roughly 2,000 ppm many species close their stomata and show leaf damage, so pushing higher wastes gas and can reduce yield rather than raise it.
Why does the calculator ask for air changes per hour?
Because a room leaks. Air exchange constantly dilutes the enriched air back towards ambient, so the concentration approaches a ceiling rather than climbing forever. Air changes per hour set both how fast that ceiling is reached and how much gas you burn just holding the target.
How long does it take to fill a room with CO2?
With a 10 litre per minute regulator, a 22.5 cubic metre room at half an air change per hour reaches 1,200 ppm in about 1.8 minutes. A sealed room fills linearly, while a leaky one approaches its ceiling exponentially, so the last few hundred ppm always take the longest.
What does Not reachable mean in the fill time box?
It means your regulator flow rate is too low to beat the leak. The room settles at a steady concentration below your target no matter how long you inject. Either raise the flow rate, seal the room to lower the air changes per hour, or lower the target.
How much CO2 does it take to hold a target concentration?
The hourly hold rate equals air changes per hour times the ppm lift times the room volume times one millionth. A 72 cubic metre room held 1,100 ppm above ambient at one air change per hour needs 79.2 litres per hour of continuous injection.
Does temperature change how much CO2 I need?
It does not change the volume of gas, because ppm is a volume ratio. It does change the mass, because warmer gas is less dense. At 20 degrees Celsius CO2 is about 1.830 kg per cubic metre, and at 30 degrees about 1.770, so the same fill weighs roughly 3 percent less.
Is a CO2 burner or a compressed gas tank better?
A tank gives clean, controllable gas with no added heat or water, which suits sealed rooms with air conditioning. A propane or natural gas burner is cheaper per unit of CO2 but adds roughly one and a half kilograms of water and a lot of heat for every kilogram of CO2 produced.
What CO2 level is dangerous for people?
Occupational exposure limits are typically 5,000 ppm averaged over an eight hour shift and 15,000 ppm short term. Concentrations above about 30,000 ppm cause headache and drowsiness quickly. Never enter an actively enriching room without ventilating it first and using a monitor.
Should I run CO2 at night?
No. Plants only fix carbon while photosynthesising, so enrichment during the dark period is wasted gas. Set the controller to inject only when the lights are on, and add a short delay after lights-on so the canopy is fully active before injection starts.
How do I convert litres of CO2 to kilograms?
Multiply by the gas density at your room temperature. At 20 degrees Celsius and one atmosphere CO2 is 1.830 grams per litre, so 100 litres weighs 183 grams. A standard 9 kg tank therefore holds roughly 4,900 litres of gas at that temperature.