Free tool
Substrate Hydration Calculator
Enter the dry weight of your substrate and the moisture content you are targeting. The calculator returns the water to add, the final wet weight, and a sterilisation time estimate for that material.
How to use these numbers
Tip
Take a handful of hydrated substrate and squeeze hard. A few drops should appear between your fingers and the ball should hold its shape. A stream means too wet; nothing at all means too dry.
Note
Below 55% the substrate feels dry and mycelium stalls. Above 78% the material compacts, air disappears, and anaerobic bacteria take over.
Caution
Hydration maths is only accurate from a dry starting weight. If you have already added water, dry a small sample and recalculate.