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Mushroom Grow Calculator

Plan a batch end to end: how much water and spawn you need, how much you'll likely harvest, and whether it actually makes money. Edit any field — everything updates live.

The Mycro Grow Calculator works out the four numbers you need before starting a batch: how much water takes your substrate to field capacity, how much grain spawn to mix in at your chosen ratio, the fresh yield to expect from a given biological efficiency, and the cost and profit per block. Free, in a browser, with no account.

1 Substrate batch

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

Dry weight before adding water.
Field capacity is ~58–62% for masters mix.
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. New to this? See the spawn ratio guide.

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

Typical mid-range — edit BE to match your strain.
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.

Bag, filter, labor, energy, etc.
Cost per block–
Total batch cost–
Cost per lb produced–

Batch summary

–
Fresh yield
–
Batch cost
–
Expected revenue
–
Profit · – margin

📧 Email me this batch plan

Your numbers, in your inbox, with a link that reopens this calculation. Handy when you are mixing substrate and the laptop is inside.

Want this to remember every batch for you? Try the free Grow Log — it tracks each batch from inoculation to harvest and works out your biological efficiency automatically. Mycro is the full version: synced across devices, with contamination patterns and real BE and cost numbers for your farm. Join the early-access list:

Ready to back us early? Become a Founding Grower — $99 once, a sign-in account today and lifetime founder pricing, fully refundable any time.

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

SpeciesTypical BENotes
Blue / Pearl Oyster75–100%+Fast, forgiving, high yield
Pink / Yellow Oyster65–90%Fast; short shelf life
King Oyster50–75%Loves supplemented sawdust
Lion's Mane50–75%Sensitive to fresh-air / humidity
Shiitake75–125%Long colonization; multiple flushes
Chestnut / Pioppino / Nameko50–75%Clustered, attractive to chefs
Reishi~30–50%Grown for medicinal use, not weight

These set the BE input above when you pick a species. To go the other way and work out the BE a batch you have already harvested actually hit, use the biological efficiency calculator: it takes your flush weights and dry substrate weight, converts a wet block weight if that is all you have, and tells you where the answer sits against the range for that species.

Frequently asked questions

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.

Can I save or print my mushroom batch plan?

Yes. The Mycro Grow Calculator can email you the finished batch plan: water per block, total spawn needed, expected yield, cost per block and profit, together with a link that reopens the calculator with the same figures so you can change one number and see what it does. It is free and needs no account.

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