What is a good biological efficiency for mushrooms?

It depends on species. Oyster commonly runs 75 to 125%+ across multiple flushes, shiitake about 30 to 74% (industrial to controlled trials), lion's mane roughly 50 to 100%, and reishi lower because it grows slow and dense. These are lifetime totals across flushes; a single first flush is lower.

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Mushroom substrate calculator

Q: How much water do I add to mushroom substrate?

Enough to reach field capacity, where a hard squeeze forces out only a few drops. By weight most fruiting substrates target about 60 to 65% moisture. To bring dry substrate of weight D to a target fraction m, add D × m ÷ (100 − m) grams of water: 400 g dry to 60% needs 600 g of water, to 65% about 743 g. Then confirm with the squeeze test.

Q: How do I calculate biological efficiency (BE)?

BE% = fresh mushroom weight ÷ dry substrate weight × 100. One kilogram of fresh mushrooms from one kilogram of dry substrate is 100% BE. Because fresh mushrooms are mostly water and the substrate is weighed dry, BE often exceeds 100% — that is expected. Always use the dry substrate weight as the denominator, never the wet weight.

Work out the water to hit field capacity, then measure the yield you got back — all cited, all free.

Two numbers decide most of a grow: whether the substrate is hydrated to the right moisture, and how much fruit you got back per unit of substrate. This page does both. The hydration math is exact; the biological-efficiency benchmarks are published starting points from Stamets, Cotter, Cornell Small Farms and Field & Forest.

1. Substrate hydration — water to add

How much water to add to bring dry substrate to field-capacity moisture. Pick a substrate for its typical target, or set your own.

Substrate

Dry substrate weight (g)

Target moisture %

Current moisture % (opt.)

2. Biological efficiency (BE%)

Fresh yield as a percentage of dry substrate weight — the standard yardstick for a flush.

Fresh yield (g)

Dry substrate weight (g)

3. Expected yield by species (inverse)

Predict total lifetime fresh yield from a species' BE range and your dry substrate weight.

Species (or custom BE)

Dry substrate weight (g)

Target BE % (custom)

Running more than one grow?

This page gives you the hydration and the BE. Flush does the rest — per-species grow trackers that log BE flush by flush across batches, plus agar, liquid-culture and grain-spawn calculators and full condition profiles for 11 gourmet and medicinal species. The trackers and advanced calculators are the paid part; everything on this page stays free.

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How to use these numbers

Weigh bone-dry substrate on a gram-accurate scale, then use calculator 1 to find the water to add.
Hydrate a predictable base like hardwood sawdust or coco coir substrate, then confirm field capacity by the squeeze test — a hard squeeze should give only a few drops.
After fruiting, weigh each flush and use calculator 2 to get BE, or calculator 3 to predict what a block should return.

FAQ

How much water do I add to mushroom substrate?
Enough to reach field capacity — a hard squeeze forces out only a few drops (~60–65% moisture by weight). Add dry weight × m ÷ (100 − m) grams of water: 400 g dry to 60% is 600 g of water. Subtract any water the substrate already holds.

How do I calculate biological efficiency?
BE% = fresh weight ÷ dry substrate weight × 100. Use the dry weight as the denominator, never wet — wet weight makes BE look far worse and ruins any comparison. Over 100% is normal.

What's a good BE for my species?
Oyster 75–125%+, shiitake ~30–74%, lion's mane ~50–100%, reishi lower (slow, dense). Calculator 3 turns a species range into a predicted yield for your block size.

Sources

Stamets, Growing Gourmet and Medicinal Mushrooms (Ten Speed Press, 2000) — moisture targets, species BE
Cotter, Organic Mushroom Farming and Mycoremediation (Chelsea Green, 2014) — substrate recipes, low-tech tek
Cornell Small Farms mushroom program & BMP (Gabriel & Mudge); Field & Forest grower guides
Bermúdez-Bazán et al., PLOS One 2024 (PMC11575786) — shiitake BE: 30–50% industrial, 59–74% controlled supp-sawdust trials

Hydration math is exact; BE ranges are benchmarks — tune to your species, strain, substrate, and how many flushes you count.