CVG & monotub calculator
Coco coir, vermiculite, and gypsum, scaled from the classic one-brick recipe (650 g coir, 8 qt vermiculite, 1 cup gypsum) to fit your tub and spawn ratio.
Measure your tub's inside floor. Tapered tubs are smaller at the bottom than at the rim.
Add water in stages and stop at field capacity: a hard squeeze gives a few drops, not a stream. Jar count assumes quart jars about ¾ full.
New to CVG? Read: hitting field capacity every time →
How this calculator works
The calculator multiplies your tub's inside floor area by the bed depth to get the total bed volume in quarts (231 cubic inches per gallon, so 57.75 per quart). It splits that bed into spawn and substrate using your ratio, then scales the classic one-brick recipe to the substrate share.
One batch of 650 g coco coir, 8 qt vermiculite, 1 cup gypsum, and about 4.5 qt of boiling water makes roughly 15 qt of finished CVG. Coir bricks vary, so treat the water figure as a starting point and finish with the squeeze test.
Common questions
How much CVG do I need for a 66 qt monotub?
With a 4 inch bed and a 1 : 2 spawn ratio, a 66 qt tub holds about 18 qt total: roughly 12 qt of CVG and 6 qt of grain spawn. That is a little under one 650 g brick batch.
What spawn to substrate ratio should I use?
1 : 2 is a common default. More spawn (1 : 1) colonizes faster and resists contamination better. Less spawn (1 : 3 or 1 : 4) stretches your grain but takes longer.
Do I need gypsum in CVG?
Gypsum adds calcium and sulfur and helps keep the mix from clumping. It's cheap and standard, but small batches without it still work.
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