Calculator
Formula Used
How to Use This Calculator
- Enter your cylinder fill amount from the label (lb or kg).
- Set a flow rate and unit based on your regulator or controller.
- Choose run hours, duty cycle, and days per week.
- Add waste/leak and reserve buffers for safer planning.
- Press Calculate to see duration and depletion date.
- Use the download buttons to save your result as CSV or PDF.
Example Data Table
| Scenario | Tank | Flow | Hours/day | Duty | Days/week | Waste | Reserve | Estimated calendar days |
|---|---|---|---|---|---|---|---|---|
| Small tent | 10 lb | 20 g/hr | 6 | 60% | 6 | 5% | 10% | ~63 |
| Medium greenhouse | 20 lb | 35 g/hr | 8 | 100% | 6 | 5% | 10% | ~32 |
| High demand | 50 lb | 1.6 lb/day | 12 | 100% | 7 | 10% | 10% | ~51 |
Operational Notes for CO2 Refill Planning
Why tank mass is the best starting point
CO2 cylinders are rated by filled mass (lb or kg), so runtime is best estimated from grams available, not the gauge needle. Pressure is strongly temperature dependent, and it stays relatively high until the cylinder is nearly empty. Using mass avoids false confidence near depletion.
Choosing a flow rate that matches your strategy
Flow is usually set by a regulator or controller, then adjusted to reach a target ppm during lights-on. Higher ventilation, frequent door openings, or oversized exhaust fans increase required flow. If you measure ppm, record a stable “typical” flow in g/hr and update it each crop cycle.
Run hours and duty cycle drive consumption
Most growers dose during the photoperiod only. Duty cycle matters when a controller pulses the solenoid to hold ppm. For example, a 40 g/hr setpoint at 8 hours with a 60% duty uses 192 g/day before losses. Small changes in duty quickly add up over weeks.
Account for leaks, purge losses, and reserves
A modest waste factor (3–10%) helps cover micro‑leaks, line purges, and regulator drift. A reserve (5–15%) prevents unexpected empty cylinders during critical flowering or fruit set. Track refill dates and adjust these buffers until predicted and actual runtimes align.
Worked example using this calculator
Example: 20 lb tank = 9,072 g. With 10% reserve, usable CO2 ≈ 8,165 g. If flow is 35 g/hr for 8 hours, daily base use is 280 g/day. With 5% waste, daily use ≈ 294 g. Running 6 days/week gives calendar duration ≈ 32 days (8,165 ÷ (294 × 6/7)).
FAQs
1) Does cylinder pressure tell me how much CO2 is left?
Not reliably. CO2 pressure changes with temperature and stays high until near empty. Use filled mass and consumption rate for planning, then keep a small reserve for safety.
2) What flow unit should I pick?
Choose the unit your regulator or plan uses. The calculator converts everything to grams per hour internally, so results stay consistent across g/min, g/hr, lb/day, and kg/day.
3) What is duty cycle and why is it important?
Duty cycle is the average on-time percentage for dosing. A controller that opens the solenoid half the time has a 50% duty cycle, which roughly halves consumption versus continuous flow.
4) How do I estimate waste or leaks?
Start with 5% if you are unsure. If your real runtime is shorter than predicted, increase waste. If runtime is longer, reduce it. Fix obvious leaks before relying on a higher factor.
5) Why does the calculator show operating days and calendar days?
Operating days count only the days you dose. Calendar days include off-days based on your weekly schedule, which is more realistic for refill planning.
6) Can I use this for compressed air or other gases?
It’s tuned for CO2 mass fills and typical greenhouse dosing. Other gases may use different cylinder ratings and behaviors, so the estimates may be inaccurate.
7) How can I make the estimate more accurate over time?
Log each refill date, setpoint, and ventilation pattern. Update flow, duty, and waste with your observed data. After a few cycles, your inputs will closely match your real runtime.