How much headspace do I need in my fermenter?

At least 20-25% headspace above the beer volume is recommended. Vigorous fermenters like wheat beers or Belgian strains may need 30-35%. A blow-off tube can help if headspace is tight.

What happens if my fermenter is too small?

Krausen can push through the airlock, creating a mess and potentially introducing contamination. Use a blow-off tube if headspace is limited, and always size your fermenter with adequate room.

Should I use a blow-off tube?

A blow-off tube is recommended for vigorous fermentations, high-gravity beers, or when headspace is limited. Connect tubing from the fermenter lid to a jar of sanitiser solution.

Does fermenter shape affect fermentation?

Conical fermenters allow easy yeast harvesting and trub removal. Bucket fermenters are affordable and easy to clean. Carboys allow visual monitoring. Shape does not significantly affect flavour in homebrewing.

Is glass or plastic better for a fermenter?

Both work well. Glass carboys are easy to clean and do not scratch, but are heavy and breakable. Food-grade plastic buckets and PET carboys are lightweight and safer. Stainless steel conical fermenters are premium but expensive. Choose based on your budget and handling preference.

BrewCalcs

Fermenter Size Calculator — Brewing Equipment

Calculate fermenter volume needed including headspace for krausen.

Batch Size

Volume of wort into fermenter

Headspace

Beer Style / Yeast Type

How We Calculate This

Fermenter Sizing

The minimum fermenter volume is: Fermenter Size = Batch Size x (1 + Headspace %). The headspace percentage includes room for krausen (the foam layer during active fermentation) which varies by yeast strain and beer style.

Krausen Considerations

Wheat beers and Belgian styles produce the most vigorous krausen, sometimes doubling the volume temporarily. Standard ales produce moderate krausen, while lagers are typically calmer. Always err on the side of more headspace.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.