Biological Efficiency Calculator
Calculate biological efficiency (BE %) from your fresh harvest and dry substrate weights, then benchmark it against typical bands for your species.
Inputs
Free account, no credit card. You'll come right back here.
How the formula works
Biological efficiency (BE) is the standard quality metric for a mushroom grow. It's the ratio of fresh mushroom yield to dry substrate weight, expressed as a percentage:
- BE % = (fresh mushroom weight ÷ dry substrate weight) × 100
BE is a conversionmetric, not a raw yield metric. Two grows with the same yield can have very different BE values if one used twice the substrate. That's the point — BE lets you compare runs across different batch sizes, species, and teks on equal footing.
Fresh weight is used (not dry mushroom weight) because mushrooms are roughly 90% water by mass. Using dry yield would understate the actual substrate-to-fruit conversion by an order of magnitude and wouldn't match how every other source reports the number. Always weigh mushrooms within an hour of harvest before they start dehydrating.
BE values above 100% are normal and expected for many species — mushrooms accumulate water from the surrounding humidity beyond what the substrate originally held, so the fresh-weight ratio routinely exceeds 1:1. Oyster grows commonly hit 150% total BE; well-tuned runs push past 180%.
Worked example
Example: a 500 g dry CVG monotub yields 500 g of fresh mushrooms across all flushes.
- BE = (500 ÷ 500) × 100 = 100%
Interpretation depends on the species. For oysters (typical band 100–185%), 100% is right at the bottom — a below-target run. For shiitake (typical band 75–125%), 100% is right on the average. Same yield, very different verdicts.
This is why a raw weight number on its own isn't enough to know whether a grow went well. BE plus species context is.
When to use this calculator
BE tells you how efficiently your substrate converted to mushrooms — full stop. It's the cleanest single number for comparing grows because it normalizes for batch size. A 5 lb tub at 120% BE was a better grow than a 20 lb tub at 80% BE, even though the bigger tub produced more mushrooms.
What BE doesn't tell you: how long the grow took, whether it contaminated mid-run, how many flushes you got, or whether the mushrooms were the right size and quality. A 90% BE across three healthy flushes over six weeks is a different story than 90% BE from one giant aborted flush. Track BE alongside time to harvest, contamination rate, and flush count — none of these replace each other.
Species matter, a lot.Oyster mushrooms routinely hit 150% total BE on CVG or straw because they're aggressive primary decomposers. Shiitake on hardwood typically tops out around 100–125%. Reishi rarely cracks 70% — it's a slow, dense mushroom that puts more energy into making chitin than into water accumulation. Comparing your reishi BE to an oyster grower's BE is meaningless.
Use BE as a comparison tool, not an absolute target.Track your own BE across grows of the same species and look for the trendline. If your oyster BE drops from 160% to 110% over three runs, something changed — maybe your culture is degrading, your substrate prep is off, or your fruiting environment is drier than before. The number itself matters less than the direction.
The flush decline curve.First flush is typically 40–60% of total BE, second flush 25–35%, third flush 10–20%, and anything beyond that is bonus. If your first flush is only 20% of total BE, your fruiting conditions probably weren't triggering a strong initial pin set. If your first flush is 80% of total and the rest is nothing, the substrate is drying out or running out of nutrition between flushes.
Frequently asked questions
Why is BE > 100% possible?
Because mushrooms aren't made only from substrate — they pull water vapor from the surrounding air during fruiting. Mushrooms are roughly 90% water by mass, and a humid fruiting chamber keeps adding moisture as they grow. So a 500 g substrate routinely produces 600–900 g of fresh mushrooms across multiple flushes. That's 120–180% BE. It doesn't violate conservation of mass — it just means the dry mass of the mushroom is small compared to the water it accumulated.
Should I weigh wet or dry substrate?
Dry. Always dry. BE is defined against dry substrate weight because hydration varies wildly — a wet CVG block at 1.6× hydration weighs 2.6× the dry weight, and using wet weight would make every BE number look 60% lower than it should. Weigh your coir, vermiculite, gypsum, and dry grain spawn equivalent before hydration, sum them, and use that. If you forgot, work backwards from your hydration ratio.
What BE should I aim for as a beginner?
For oysters on CVG, a first-time grower hitting 80–100% total BE is doing fine — that's the lower edge of the typical band but well within reasonable for a learning run. For shiitake on hardwood blocks, 60–80% on your first attempt is normal. Don't chase a specific number on grow #1; chase consistency. Three consecutive grows in the same range is a stronger signal than one high-BE outlier.
Why is my BE lower than expected?
The usual suspects in order: under-hydrated substrate (mushrooms can't pull water out of nothing), low fruiting humidity (same problem from a different angle), insufficient fresh air exchange causing aborts, harvesting too early before the second and third flushes pin, contamination eating substrate before the mycelium could colonize it, or a tired culture that's been transferred too many generations. Check your environmental log against your species' target ranges first — that catches most of these.
Related resources
- Spawn-to-bulk calculator — Match grain spawn to bulk weight for your next grow.
- CVG substrate calculator — Get exact substrate weights for your next batch.
- Species database — Typical BE ranges and growing parameters for every species in the app.
Want to log every batch and let First Flush do this math automatically? Create a free account or see what comes with First Flush Pro.