Mushroom Spawn Requirement Calculator

Work out mushroom spawn requirement instantly with clear inputs, formula shown and shareable results.

About Mushroom Spawn Requirement Calculator

Spawn is added at 1.5-3% of wet substrate weight for oyster mushrooms and 0.5-1% for button mushroom compost. Higher rates colonise faster and reduce contamination risk but cost more, so the rate is a trade-off between spawn cost and the risk of losing a batch.

Formula

Spawn requirement

Spawn (kg) = substrate weight x spawn rate %; bags = substrate / substrate per bag

Worked example

With the default values below, Mushroom Spawn Requirement Calculator returns Spawn Required of 20.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Substrate Weightminimum 0.1 kg: 1,000 kg
Spawn Rateaccepts 0.1–10 % of wet substrate: 2 % of wet substrate
Substrate Per Bagminimum 0.1 kg: 2 kg
Spawn Priceminimum 0 per kg: 90 per kg

Results

Spawn Required: 20.00
Bags Or Beds Prepared: 500
Spawn Per Bag: 0.0400
Spawn Cost: $1,800.00

Step by step

1Values used
2Spawn requirement
3Spawn Required= 20.00
4Bags Or Beds Prepared= 500
5Spawn Per Bag= 0.0400
6Spawn Cost= 1,800.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Does more spawn always mean faster colonisation?

Up to a point. Above about 4% the extra spawn generates heat that can kill the mycelium in the bag centre, and the cost is no longer repaid.

How fresh must spawn be?

Use within 2-4 weeks of production, stored at 2-4 C. Old spawn has reduced vigour and colonises slowly, which is when competitors like Trichoderma take hold.