Spawn Ratio Calculator
Work out how much grain spawn to mix into your substrate — or how much substrate a given amount of spawn will colonize — at any ratio you choose.
Spawn ratio is a speed-versus-cost decision, not a species rule. More spawn colonizes faster and shrugs off contamination; less spawn stretches your grain further but gives contaminants a longer window. The calculator shows the trade-off for whatever ratio you set, with 1:5 as the usual starting point.
Ratio is a speed-versus-cost choice, not a species rule. 1:5 (20%) is the usual default; more spawn colonizes faster and shrugs off contamination, less spawn stretches your grain further.
How to use it
- Choose a direction. You have substrate and want spawn, or you have spawn and want to know how much substrate it covers.
- Enter the amount. The weight of whichever one you already have, in metric or imperial.
- Set the ratio. From heavy (fast, more grain) to lean (economical, slower).
- Read the result. The other quantity, the spawn-to-substrate proportions, and a note on speed versus grain cost.
Questions
What spawn ratio should I use?
1:5 (about 20% of substrate weight) is the usual default. More spawn colonizes faster and resists contamination; less stretches your grain further but is slower.
Does more spawn mean faster colonization?
Yes. More spawn points mean the mycelium has less distance to cover, so it colonizes faster and gives contaminants a smaller window.
Does spawn ratio depend on the species?
Not really — it's mostly a speed-versus-cost choice. 1:5 works across the common gourmet species.
Is the ratio by weight of hydrated substrate?
Yes, spawn as a share of the hydrated substrate's weight. The tool shows what percentage of the finished mix is spawn.