Mushroom Substrate Volume Calculator

Calculating substrate volume for mushroom cultivation

Substrate is the nutrient material mushrooms grow on. The volume you need depends on your container type and the substrate recipe. Getting the right volume ensures proper colonization and maximizes yield.

Volume formula for common containers:

Rectangular tray: Volume (liters) = Length (cm) × Width (cm) × Depth (cm) ÷ 1000

Round bucket: Volume (liters) = π × Radius² × Height ÷ 1000 (all in cm)

Grow bag: Use the bag dimensions (typically 30×18×60 cm or similar). Fill to about 60–70% of bag height to allow gas exchange space.

Dry weight from volume:

The volume you measure is the finished bed sitting in the container, already wet. So the useful number is not the density of a dry pile, it is how much dry material ends up in each litre of that finished bed.

The last column is not an independent measurement, it is the first divided by (1 − moisture). Quote them separately and they drift apart, which is exactly what this page used to do.

Pellets and sawdust share a row on purpose. A hardwood fuel pellet is compressed sawdust and nothing else, so once it has soaked and burst it behaves identically. The pellet is only denser while it is still a pellet, and that is a state your substrate never fruits in.

The coir figure is worth pinning down because coir is sold compressed. A standard 650 g brick expands to roughly 8 quarts hydrated, which is 650 g of dry coir spread through 7.6 litres of finished bed. That is the 80 g per litre in the table.

Worked example — 5-gallon bucket of straw:

A 5-gallon bucket is about 28 cm across, and filling it 31 cm deep leaves room for the lid and the drainage holes. Enter 28 for the diameter, 0 for the width, and 31 for the depth.

Volume: π × 14² × 31 = 19,088 cm³ = 19.09 liters Dry straw: 19.09 × 70 = 1,336 g, call it 1.34 kg Water: 1,336 ÷ 0.28 × 0.72 = 3,436 g, so about 3.4 liters Hydrated: 1,336 + 3,436 = 4,772 g ≈ 4.77 kg, which checks out at 250 g per litre

Substrate depth guidelines:

Supplementation: Many cultivators add wheat bran, soy hulls, or gypsum at 5–20% of dry substrate weight to increase yields. For oyster mushrooms on straw, adding 10% soy hulls can increase yield by 20–30%. Always pasteurize or sterilize supplemented substrates to prevent contamination.

Yield expectations: Count on 20–30% of the wet substrate weight across the whole run, not from one harvest. A 5 kg block of oyster gives 1–1.5 kg of fresh mushrooms over two or three flushes, and the first flush is the big one at roughly 15% of the block. Each flush after that is noticeably smaller, and by the third most growers have decided the space is worth more to the next block.