Fruiting Chamber Size Calculator
Calculate fruiting chamber dimensions for mushroom growing from substrate volume and species.
Returns chamber size, FAE holes, and humidity surface area.
A properly sized fruiting chamber provides the right balance of fresh air exchange (FAE), humidity, and growing space for mushroom cultivation. The two most common types are the Shotgun Fruiting Chamber (SGFC) and the Monotub.
Chamber Volume Rule
A good rule of thumb:
Chamber Volume = Substrate Volume × 4 to 6
This ratio ensures adequate airspace above the substrate for proper air exchange and humidity maintenance. Too small and CO2 builds up (causing leggy, thin mushrooms). Too large and humidity is harder to maintain.
Monotub Sizing Guide
| Substrate Amount | Tub Size | Dimensions (approx.) | Yield Estimate |
|---|---|---|---|
| 2–3 lbs dry | 32 qt (30 L) | 21" × 15" × 9" | 1–2 lbs fresh |
| 4–6 lbs dry | 58 qt (55 L) | 23" × 17" × 12" | 2–4 lbs fresh |
| 6–8 lbs dry | 66 qt (62 L) | 25" × 18" × 13" | 3–5 lbs fresh |
| 8–12 lbs dry | 105 qt (100 L) | 34" × 20" × 13" | 5–8 lbs fresh |
SGFC Sizing
The classic SGFC uses a clear tote with 1/4" holes drilled on a 2" grid on all six sides. Substrate sits on perlite for humidity:
Perlite Depth = 4–5 inches Air gap above substrate = at least 6 inches
Substrate Depth
For monotubs, the ideal substrate depth is 3–5 inches (7.5–12.5 cm). Thinner beds dry out too fast. Thicker beds risk anaerobic conditions and contamination in the center.
Worked Example
Growing oyster mushrooms with 5 lbs dry substrate (bulk weight ~15 lbs hydrated):
- Hydrated substrate volume ≈ 10 quarts
- Chamber volume = 10 × 5 = 50 quarts → 58 qt tub
- Substrate depth at 23" × 17": 10 qt / (23 × 17 / 231) = ~5.9 inches (good)
- Expected yield: 2–4 lbs fresh per flush, 2–3 flushes
Environmental Parameters
| Species | Temp (°F) | Humidity | FAE Need | Light |
|---|---|---|---|---|
| Oyster | 60–75 | 85–95% | High | 12 hr indirect |
| Shiitake | 55–70 | 80–90% | Moderate | 12 hr indirect |
| Lion’s Mane | 60–75 | 85–95% | High | 12 hr indirect |
| King Oyster | 55–65 | 85–95% | Moderate | 12 hr indirect |
| Reishi | 70–80 | 85–95% | Low | 12 hr indirect |
Humidity Maintenance
For a monotub, drill holes and cover with micropore tape to control FAE. Misting 2–3 times daily maintains surface humidity. For SGFCs, the perlite layer plus fanning provides passive humidity and air exchange.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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