Grow Light DLI Calculator
Daily light integral from PPFD and hours — and the runtime or intensity a crop needs.
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CO2 Supplement Calculator
Grams of CO2 to lift a tent or room to target ppm, the ppm each gram buys, and how long a tank or burner supply lasts.
CO2 Supplement Calculator
Chlorova · updated for 2026
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The ppm-per-gram figure assumes a closed, well-mixed volume near room temperature, so leaks, active extraction and tall rooms all push the real number lower, meaning this answer is the minimum charge rather than a guaranteed reading. One pound is 454 grams and a full day's use is guessed from your own controller habits, so weigh tanks before and after a logged day to learn your real burn rate. Never enter a sealed tent that has been running CO2 without ventilation: the gas is odorless, invisible and dangerous at the concentrations plants tolerate, and a personal monitor plus working smoke and carbon monoxide alarms are the price of admission for any supplementation setup.
Supplemental CO2 is the cheapest yield a sealed tent can buy, but only when the dose is metered rather than guessed, because the gap between ambient air at roughly four hundred parts per million and the twelve hundred a hungry canopy wants is a matter of grams, not buckets. This calculator sizes that lift from tent dimensions and a target reading: the ppm each gram buys in your air volume, the charge to reach target, and how many days the tank or burner supply on hand will last at your expected use.
Dosing a Tent in Steps
- Choose the CO2 source so the right safety note prints with results.
- Measure the grow space length, width and height in feet.
- Enter the ppm the monitor reads now, ambient is near 420.
- Set the target ppm, twelve hundred suits most light-hungry crops.
- Weigh the supply on hand in pounds of CO2, not the tank.
- Estimate daily use in grams from logged runs if you have them.
- Read grams for the lift first, then days of supply.
- Re-verify with your own monitor after the first timed dose.
How Grams Become Parts Per Million
A gram of CO2 expands to roughly half a liter of gas at room temperature, and parts per million is simply that gas volume divided by the air volume times a million. So the calculator multiplies the tent's cubic feet by 28.3 to get liters, then divides the half-liter-per-gram figure by it: a 96 cubic foot tent holds about 2,718 liters, making one gram worth roughly 204 ppm.
The lift is then a subtraction and a division. Target minus starting ppm gives the gap, divided by the ppm-per-gram figure reports the grams to fill it. Supply longevity converts pounds to grams at 454 per pound and divides by the expected daily burn, rounding up because a tank that dies mid-day is a tank you measured too optimistically. Empty, zero or reversed ppm entries return a dash rather than a negative dose.
Worked Example: A 4 by 4 Tent on a 5 lb Tank
- The tent measures 4 by 4 by 6 feet, so 96 cubic feet.
- Ninety-six cubic feet is 96 times 28.3, about 2,718 liters.
- One gram of CO2 in that air moves roughly 204 ppm.
- The lift from 420 to 1,200 is a 780 ppm climb.
- Dividing 780 by 204 says about 3.8 grams to get there.
- A five pound tank carries 5 times 454, so 2,270 grams.
- At a guessed 20 grams a day that reads 114 days.
- Real tents leak, so log the tank weight after week one.
- If the true burn is 40 grams a day, halve that runway.
Common Targets and Rough Uses
Typical enrichment targets by crop style with the ppm-per-gram figure for a standard small tent, the same arithmetic the results panel performs. Bigger rooms scale inversely, so halve the tent column to roughly double a 64 cubic foot space's value.
| Setup | Volume | ppm per gram | Common target |
|---|---|---|---|
| 2x2x4 Cube tent | 16 cu ft | 1,227 | 800-1,000 ppm |
| 4x4x6 Tent | 96 cu ft | 204 | 1,100-1,300 ppm |
| 4x8x7 Room | 224 cu ft | 88 | 1,000-1,200 ppm |
| Greenhouse bay | 1,000+ cu ft | under 20 | 700-900 ppm |
Key Terms
- ppm
- Parts per million, the volume fraction the CO2 monitor displays.
- Ambient air
- Ordinary outdoor air at roughly 420 ppm, the baseline for any lift.
- Solenoid
- The valve a controller clicks to pulse gas into the tent on schedule.
- Burn rate
- Grams of CO2 consumed per light hour, found by weighing tank before and after.
- Saturation point
- The ppm past which extra gas buys no more photosynthesis, usually near 1,500.
Lessons from Grow Rooms That Get It Right
- The monitor is the calculator, because tent math assumes a sealed box while real fabric tents leak around zippers and duct ports, so the ppm reading and the regulator dial win over any arithmetic.
- Gas only pays while lights run, so a timer aligned to the light schedule wastes far less than continuous dosing, since a dark canopy stops taking CO2 within minutes.
- Two small tanks beat one big one in tight spaces, because a 20-pound cylinder in a closet is a tipping hazard while two 5-pounder swaps keep the run alive mid-cycle.
- Heat is the hidden cost of burners, as a propane burner making 1,200 ppm in a sealed room is also making steam and warmth your HVAC then pays to remove.
- Ventilation and enrichment are the same conversation, because strong extraction that protects vapor-pressure deficit also strips the gas you paid for, so tune both against the monitor.
Common Mistakes & Fixes
- Dosing a room with open extraction and judging the calculator wrong for it.
- Weighing the steel tank instead of the gas, since tare changes nothing but is tempting.
- Running CO2 all night when a dark canopy takes up none of it.
- Skipping the monitor in a sealed space where the safe plant level is unsafe for people.
- Setting targets at 2,000 ppm past the saturation point, paying for gas that does nothing.
- Confusing liters-per-day regulator ratings with grams when sizing the daily burn.
When to Use This (and When Not To)
Use it when the tent is sealed, lights run hard enough to saturate a canopy, and the question is how many grams or how long the tank lasts. If you cannot keep a closed environment, skip enrichment entirely and grow with fresh air instead, and pair this sizing with the grow-light DLI calculator to confirm the light actually justifies the gas before buying another cylinder.
CO2 Supplement Calculator: Frequently Asked Questions
How much CO2 does a grow tent need?
Most light-hungry crops plateau near 1,200 ppm, roughly triple ambient air, and a closed 96 cubic foot tent needs only about four grams to climb from ambient to that level. The tank you already have almost certainly holds hundreds of those lifts.
How many grams of CO2 per cubic foot?
Near a tenth of a gram per cubic foot per hundred ppm, or about half a liter of gas per gram spread through the air volume. A 96 cubic foot tent reads about 204 ppm per gram, while a 224 cubic foot space sees closer to 88.
How long does a 20 lb CO2 tank last?
At twenty pounds it holds about 9,070 grams, so a modest tent burning twenty grams a day runs roughly 450 days, while a burner-style room at 300 grams a day drains it in a month. Log the weight after one week to find your real rate.
Is fermentation enough for a small tent?
Sugar-and-yeast buckets produce a slow trickle, sometimes useful for a single cube tent but far short of a controller-driven schedule in a full-size tent. Measured tank or burner output is what holds a steady ppm under lights.
Can CO2 hurt plants?
Past roughly 1,500 ppm most crops simply stop responding rather than thriving, and the wasted gas can coincide with heat and humidity swings that do cause trouble. The ceiling is economic long before it is toxic, which is why saturation, not maximum, is the goal.
Do I need a controller or will a timer do?
A timer synced to the lights works for tight tents, but a sensor controller holds ppm exactly, which matters in leaky fabric setups. Either way, a monitor and alarms in the room are mandatory, because CO2 at plant-safe levels is invisible and dangerous to people.
Sources & Further Reading
- Carbon Dioxide Enrichment for Controlled Environment Agriculture — Purdue University Extension. Basis for target ppm ranges and saturation guidance.
- CO2 Injection for Greenhouses and Grow Rooms — Utah State University Extension. Source of burner safety and dosing-timing recommendations.
- Safety in Confined Growing Spaces — Michigan State University Extension. Underpins the monitor and alarm cautions on this page.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
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