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CO₂ Enrichment Calculator
Find the CO₂ level that suits your crop and light, how much CO₂ your space needs to hold it, and what the research says you gain
Room & Units
Everything that leaks from the tent ends up in this room.
Crop & Light
0 means lights off.
CO₂ is added only while the lights are on.
The area actually covered by leaves, every tier included. Filled in from length × width (× tiers in Advanced); 0 for an empty room.
Air Exchange & CO₂ Levels
Filled in from the space type. Your own value replaces the preset; the space type is kept.
Outdoor air averages about 425 ppm (2026). House air is often higher, and city air averaged about 25 ppm above the outdoor background in one study (Park 2021). Measure yours if you can.
Conditions
Leave blank for 25 °C.
Height above sea level. Leave blank for sea level.
Stacked racks: the canopy area is filled in as length × width × tiers, so count every tier. Leave blank for 1.
How much of the canopy area is leaf. Leave blank for 100%.
Your own uptake per m² of canopy at the target, used whenever the lights are on. The uptake test in Measure My Room gives this figure, converted to your target. Leave blank to use the estimate.
For greenhouses, where light changes through the day. Replaces the PPFD above for plant uptake.
For advice only.
Leakage rises roughly in step with wind speed: doubled at 4-5 m/s.
A 1994 greenhouse rule of thumb, shown beside the 630-experiment curve.
Exhaust & Vents
Leave blank for 2 minutes.
During these hours the calculator holds the outdoor level instead of enriching. They are taken as one block, with one refill to the target when the vents close.
Dosing Dynamics
The flow while dosing, as gas at room conditions.
Time to show 90% of a step change. Leave blank for 2 minutes.
Time for added CO₂ to reach the sensor. Leave blank for the space type's range.
Total width, e.g. 50 = target ± 25. Leave blank for 50.
Sensor
Leave blank for 50 ppm.
Leave blank for 3%.
Room Around the Tent
Leave blank for 30 m³.
Leave blank for 0.5, an ordinary room.
Measure My Room
Air-change test, lights off and nothing added (plants mask the result with the lights on).
Plant-uptake test, lights on and nothing added.
Press Calculate: the result appears under Measured in your space, converted to your target.
Enter your space's length, width and height; everything else starts from a sensible value you can change.
How this is calculated · Sources
The model in plain words
- Volume of the space: length × width × height.
- Gas density from temperature and elevation (ideal gas; air pressure from the US Standard Atmosphere). At 25 °C and sea level 1 litre of CO₂ weighs 1.799 g.
- Fill: raising the space from the incoming-air level to the target. 1 ppm in 1 m³ is 1 mL of gas at any temperature; only its weight changes.
- Leakage: air changes per hour × volume × (target − incoming air). The same well-mixed formula appears in 9 published formulations (8 peer-reviewed, 1 thesis).
- Plant uptake (estimate): canopy area × a measured canopy light and CO₂ response (Nederhoff & Vegter 1994), with a CO₂ compensation point of 50 ppm, anchored to measured lettuce, fruiting-crop and cannabis canopies and capped at 10 g/m²/h.
- Hold rate and daily total: leakage plus uptake while the lights are on, plus the fill, the refill after vent-open hours, exhaust-burst refills and any hours spent holding the outdoor level.
- CO₂ use efficiency: the share of the CO₂ added that the plants fix (Kozai 2013).
- Expected gain: the crop's published trial range, and the dose-response curve of a 630-experiment meta-analysis (Poorter et al. 2022).
Key assumptions
- One well-mixed space; the real gas differs from an ideal gas by about 0.5%, far below sensor accuracy.
- Night respiration is not credited. The carry-over option credits only CO₂ left from the previous day's enrichment after leakage decay. With 24-hour lighting there is no dark period, so the space is filled once at start-up, not every day.
- Vent-open hours are taken as one block within the lit period: the space falls to the incoming level and is refilled once when the vents close.
- Grow-tent leakage (1.5 air changes per hour) is assumed: no published measurement exists. Measure yours with the air-change test.
- The uptake model is fitted up to about 700 µmol/m²/s and is extrapolated above that.
- The gain curves rest mostly on 330-780 ppm data; above about 1,000 ppm they are low reliability.
- Gains are against air at the incoming-air level unless stated. Pot-study results under 5 litres are never shown as expected gains.
Health reference levels used
- 1,000 ppm: the most common indoor-air guideline value (43 guidelines, mostly about ventilation and odour, not toxicity).
- 5,000 ppm: health reference level averaged over up to 10 hours a day (NIOSH). In a 2.5-hour human study only exhaled CO₂ rose; no symptoms or performance change.
- 30,000 ppm: 15-minute health reference level (NIOSH). Mild headache, sweating and breathlessness after about 1 hour at around 3% (HSE); submarine crews kept at 3% were only slightly affected (NIOSH). At 2%, people at rest for 4 hours showed no acute effects (Maniscalco 2022); headache and breathlessness appeared at 4% (Ryan 2022, 2025).
- 40,000 ppm: "immediately dangerous" level (NIOSH). Headache and breathlessness within 12-30 minutes in human studies.
Evidence key
Peer-reviewed study; Meta-analysis or review; Conference paper (peer-reviewed); Thesis (examined); Dissertation (not peer-reviewed); Reference data (physical constants); Standard method (engineering standard, not peer-reviewed); Government research data. Figures marked "estimate" are calculations or syntheses, not measurements.
Hydro Oasis • CO₂ Enrichment Calculator