How much headspace do I need in my kettle?

A minimum of 20% headspace above the pre-boil volume is recommended to prevent boil-overs. For vigorous boils or high-gravity worts with lots of hot break, 25-30% is safer.

What is a typical boil-off rate?

Most homebrewers lose 3-5 litres per hour to evaporation, depending on kettle diameter, heat source intensity and whether you use a lid. Measure your own system by noting volume before and after a timed boil.

What size kettle do I need for a 23-litre batch?

For a standard 23L batch with a 60-minute boil, you typically need a 33-40L kettle. This accounts for roughly 4L boil-off, 2L trub loss and 20% headspace.

Does kettle shape matter?

Wider kettles have higher boil-off rates due to greater surface area. Taller, narrower kettles retain more volume but may have less vigorous boil circulation. A moderate width-to-height ratio works best for most homebrewers.

Can I use a kettle that is too large?

A larger kettle is generally fine — better too big than too small. The main considerations are: a wider kettle increases boil-off rate (more surface area), and a very large kettle with a small batch may require more energy to reach and maintain a boil.

BrewCalcs

Kettle Size Calculator — Brewing Equipment

Calculate the minimum kettle size for your batch with headspace allowance.

Target Batch Size

Final volume into fermenter

Boil Time

Boil-Off Rate

Evaporation rate per hour

Trub/Dead Space Loss

Headspace Allowance

How We Calculate This

Kettle Sizing Formula

The minimum kettle size is calculated as: Kettle Size = Pre-Boil Volume x (1 + Headspace %). The pre-boil volume equals your target batch size plus boil-off losses plus trub/dead space losses.

Accounting for Losses

Boil-off depends on your system and is typically 3-5L per hour. Trub loss is the volume of wort left behind with hops and protein sediment. Together these determine how much wort you need before the boil starts.

Frequently Asked Questions

Related Calculators

Fermenter Size Calculator

Calculate fermenter volume needed including headspace for krausen.

Mash Tun Calculator

Calculate mash tun volume needed for your grain bill and water ratio.

Boil Off Calculator

Calculate boil-off rate and total evaporation for your system.

Dead Space Calculator

Calculate and account for dead space losses in your brewing system.

Cooling Time Calculator

Estimate wort cooling time based on chiller type and water temperature.

Last updated: February 2026

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