Bioactive Substrate Calculator: How Many Quarts and Bags You Need

How the calculator works

Volume is floor length times floor depth (front to back) times layer depth, all in inches, which gives cubic inches. The calculator then converts:

• Quarts: divide by 67.2 cubic inches, the US dry quart (67.200 625 cubic inches exactly, NIST Handbook 44, Appendix C). Bagged substrate is labeled in quarts, so this is the figure to compare with the bag.
• Liters: divide by 61.02 cubic inches (1 liter is 61.023 74 cubic inches, NIST). If your bag is labeled in liters, use this figure; a dry quart is 1.101 liters.
• Cubic feet: divide by 1,728 cubic inches.
• Bags: substrate quarts divided by the bag size, rounded up.

The calculator does not add anything for settling. Loose substrate packs down once it is moistened, so if you are close to a whole bag, buy one more.

Where the defaults come from

Calculator defaults and their sources

Input	Default	Why
Floor length x depth	48 x 24 in	The nominal floor of a 4 x 2 x 2 enclosure, the most common size for adult snakes and lizards; Zen Habitats gives its standard 4 x 2 x 2 as 48 x 24 x 24 in (Zen FAQ). Replace it with your inside measurement.
Drainage layer	2 in	Josh's Frogs calls for a 2-inch false bottom under its Tropical BioBedding when you use automatic misting (Josh's Frogs). Set it to 0 for The Bio Dude's Terra Sahara, which needs no drainage layer (The Bio Dude), and for BioBedding with hand misting.
Substrate depth	4 in	Above the makers' minimums (at least 3 in for Terra Sahara, The Bio Dude; 2.5 to 3 in for Tropical BioBedding) and within the 6 inches that Zen's 4 x 2 x 2 substrate shield and Bio-Basin hold (Zen Habitats).
Bag size	10 qt	The bag size of Josh's Frogs Tropical BioBedding and of Zoo Med ReptiSoil (Zoo Med). The Bio Dude sells 6, 18 and 36 quart bags; change it to match yours.

Worked examples

Substrate and drainage for common enclosures (US dry quarts; our arithmetic)

Enclosure floor	Layers	Substrate	Bags	Drainage
48 x 24 in (4 x 2 x 2)	2 in drainage, 4 in substrate	68.6 qt (75.5 L, 2.67 cu ft)	7 x 10 qt	34.3 qt (37.8 L)
36 x 18 in (leopard gecko, desert mix)	No drainage, 3 in substrate	28.9 qt (31.9 L)	2 x 18 qt	None
18 x 18 in (crested gecko, misted tropical)	2 in drainage, 3 in substrate	14.5 qt (15.9 L)	2 x 10 qt	9.6 qt (10.6 L)
24 x 24 in (2 x 2 x 4, deep bed)	2 in drainage, 6 in substrate	51.4 qt (56.6 L)	6 x 10 qt	17.1 qt (18.9 L)
72 x 24 in (6 x 2 x 2)	No drainage, 4 in substrate	102.9 qt (113.3 L, 4.0 cu ft)	3 x 36 qt	None

Measure inside, not the label

Enclosure sizes are usually nominal or outside dimensions. The Bio Dude lists its Kages-built "4 x 2 x 2" at approximately 47 x 23 x 23.5 inches outside, with half-inch walls (The Bio Dude), which puts the inside floor at about 46 x 22 inches. At 4 inches deep that floor needs 60.2 quarts, not the 68.6 the nominal 48 x 24 gives, about 12% less. Measure from side panel to side panel and from the front glass or barrier to the back panel.

Check height too. The drainage and substrate together should sit below the substrate barrier, or soil spills into the door track. Our guide to the best bioactive enclosures lists each enclosure's barrier height.

Weight

The Bio Dude says an 18-quart bag of Terra Sahara averages 14 pounds (The Bio Dude), about 0.78 pounds a quart. At that rate the 68.6 quarts in the default example weigh about 53 pounds before water, rock and wood. Zen Habitats rates its stands for 75 pounds of substrate in the enclosure above; check your own stand or furniture.

Next steps

Choose a mix for your animal in our best bioactive substrates guide, then follow the layer-by-layer steps in how to set up a bioactive enclosure. If you have not chosen the enclosure yet, start with the enclosure size guide.