How much water to add to mushroom substrate?

To reach field capacity (about 60% moisture), add water equal to roughly 1.5x the dry substrate weight, so dry substrate plus water ends near 2.5x the dry weight. Water = M/(1-M) x dry weight, where M is the target moisture fraction.

What is biological efficiency for mushrooms?

Biological efficiency (BE) is fresh mushroom yield divided by dry substrate weight, as a percentage. Oyster mushrooms commonly hit 75-100%+, while king oyster and lion's mane are often 50-75%.

What spawn ratio should I use?

A common spawn rate is 10-30% of the hydrated substrate weight. 20% equals a 1:5 spawn-to-substrate ratio. Higher spawn rates colonize faster and resist contamination but cost more.

Mushroom Grow Calculator — substrate, spawn ratio, yield & profit

1 Substrate batch

Hydrate dry substrate (sawdust, soy hull / "masters mix", straw pellets) to field capacity.

Dry substrate per block Dry weight before adding water.

Target moisture % Field capacity is ~58–62% for masters mix.

Number of blocks / bags In this batch.

Water to add per block–

Hydrated weight per block–

Total dry substrate–

Total water–

Total hydrated substrate–

2 Spawn

Grain (or sawdust) spawn as a percentage of the hydrated substrate weight.

Spawn rate % 10–30% typical · higher = faster colonization, less contam.

Spawn-to-substrate ratio For your spawn rate.

Spawn per block–

Total spawn needed–

3 Expected yield

Estimated fresh harvest across all flushes, from biological efficiency (fresh weight ÷ dry substrate).

Species (sets a typical BE) Typical mid-range — edit BE to match your strain.

Biological efficiency (BE) % Oyster 75–100%+ · King/Lion's Mane 50–75% · Shiitake 75–125%.

Expected fresh yield per block–

Total expected fresh yield–

4 Cost & profit

Your real cost per block and per pound — so you can price wholesale with confidence.

Dry substrate cost

Spawn cost

Other cost per block ($) Bag, filter, labor, energy, etc.

Sale price

Cost per block–

Total batch cost–

Cost per lb produced–

Batch summary

–

Fresh yield

–

Batch cost

–

Expected revenue

–

Profit · – margin

Want this to remember every batch for you? Mycro logs each batch from spawn to flush, tracks contamination, and turns months of batches into the real BE and cost numbers for your farm. Join the early-access list:

How the math works

No black box — here's exactly what the calculator does.

Substrate hydration (field capacity)

To hit a target moisture content M, water added = M ÷ (1 − M) × dry weight. At 60% moisture that's 1.5× the dry weight in water, so a hydrated block ends around 2.5× its dry weight. Assumes a near-dry starting substrate (sawdust, soy hull pellets, dried straw). "Field capacity" means fully hydrated but not dripping when squeezed firmly.

Spawn ratio

Spawn rate here is a percentage of the hydrated substrate weight. 20% equals a 1:5 spawn-to-substrate ratio. More spawn colonizes faster and crowds out contamination, at higher cost.

Yield & biological efficiency

Biological efficiency is fresh mushroom weight ÷ dry substrate weight × 100%, summed across flushes. We estimate fresh yield as dry substrate × BE. BE varies widely with species, strain, substrate, and conditions — treat the presets as starting points and dial in BE from your own results (which is exactly what Mycro tracks).

Cost & profit

Batch cost = dry substrate cost + spawn cost + other per-block costs. Revenue = expected fresh yield × sale price. Cost per pound produced = total cost ÷ total fresh yield — the number to beat when you quote a restaurant.

Typical biological efficiency by species

Species	Typical BE	Notes
Blue / Pearl Oyster	75–100%+	Fast, forgiving, high yield
Pink / Yellow Oyster	65–90%	Fast; short shelf life
King Oyster	50–75%	Loves supplemented sawdust
Lion's Mane	50–75%	Sensitive to fresh-air / humidity
Shiitake	75–125%	Long colonization; multiple flushes
Chestnut / Pioppino / Nameko	50–75%	Clustered, attractive to chefs
Reishi	~30–50%	Grown for medicinal use, not weight

Ranges are general guidance gathered from common cultivation practice, not guarantees. Your mileage will vary. Mycro is for legal culinary & medicinal mushrooms only.