Mushroom Grow Bag Calculator
Scale a gourmet production block recipe — oyster, lion's mane, shiitake, chestnut, king oyster and similar edible species — across as many bags as you are making. Enter the finished hydrated weight you want per bag and the calculator works backwards to your dry ingredients and water.
Learn the method behind this calculatortotal finished = bags × finished weight per bag · water = total finished × moisture% · dry ingredients = total finished × (1 − moisture%) · each ingredient = dry ingredients × its share of the dry split
Water plus dry ingredients always equals your target finished mass.
A planning estimate, not a universal optimum. Growers commonly work somewhere around 60%, but the right figure depends on your species, substrate, bag type and process.
Full batch — 10 bags
Mushroom Grow Bag Calculator
- Bags
- 10
- Finished per bag
- 2.5 kg
- Target moisture
- 60%
Want to remember this batch? Save it to a free Hyphae Fidelity grow.
Start a free growWhat you will need
Gear suggestions live on our gear page, which carries its affiliate disclosure. The calculators stay free either way.
Scaling a gourmet production block recipe
Most gourmet growers describe a block by what it weighs when it is finished and hydrated — a 2.5 kg oyster block, a 5 lb shiitake block. That is a convenient way to buy bags and plan shelf space, but it is not how you buy ingredients. This calculator turns the finished weight you want into the dry sawdust, supplement and water you need to weigh out, then multiplies it across the batch so you can shop and mix once.
Finished wet weight versus dry ingredients
A finished block is mostly water. At 60% moisture, a 2.5 kg block is 1.5 kg water and 1 kg dry ingredients. Confusing the two is the most common scaling mistake: ordering 2.5 kg of sawdust per block would give you blocks two and a half times heavier than planned once hydrated. Keep dry ingredient weight as your ordering figure and finished weight as your production figure.
The moisture percentage formula
Moisture here is expressed as a share of the finished hydrated mass — the wet basis: moisture% = water ÷ finished mass × 100. So water = finished mass × moisture%, and dry ingredients = finished mass × (1 − moisture%). Some references quote moisture on a dry basis instead (water ÷ dry mass), which produces a larger-looking number for the same mixture, so check which basis a recipe means before copying its figure.
Batch scaling in practice
- Weigh dry ingredients for the whole batch, then mix dry before adding water.
- Add water gradually and stop short of the calculated figure if the mix already feels at field capacity.
- Fill bags by weight rather than by eye so every block is comparable.
- Write the dry ingredient weight on each bag — you will need it for biological efficiency later.
Frequently asked questions
Which species is this for?
Edible gourmet and culinary species grown on supplemented sawdust blocks — oyster, king oyster, lion's mane, shiitake, chestnut, nameko and similar.
Does it account for ingredient moisture?
No. It assumes bone-dry ingredients, which is the simplest and most transparent basis. If your sawdust is damp, you will need slightly less added water than shown.
What supplement percentage should I use?
That depends on your species, sterilisation capability and contamination risk. The default here is simply a common starting point, not a recommendation — change it to match the recipe you are following.
Does it cover sterilising the bags?
No. This tool only handles recipe arithmetic. Follow the documented instructions for whatever equipment you own for anything involving heat or pressure.
Related calculators
- Master's Mix calculator — the fixed 50:50 hardwood and soy hull version of this maths.
- Substrate hydration calculator — water to add when you start from a known dry weight.
- Spawn ratio calculator — how much grain spawn the batch needs.
- Biological efficiency calculator — measure what these blocks actually returned.
Track this batch of blocks free
Hyphae Fidelity is a free grow tracker for gourmet cultivation — log every batch, check, harvest and contamination, and see what actually works in your setup.