What is a normal boil-off rate?

Most homebrew systems lose 3-5 litres per hour, or roughly 10-15% of the pre-boil volume in a 60-minute boil. Electric systems tend to have lower boil-off rates (8-12%) than gas burners (12-18%). Knowing your rate helps you plan pre-boil volumes accurately.

Why does boil-off rate matter?

Boil-off concentrates your wort, increasing gravity and hop bitterness. If your actual boil-off differs from the recipe assumption, your OG and IBU will be off target. Recording your boil-off rate lets you adjust pre-boil volume to hit your numbers consistently.

How can I reduce boil-off?

Reduce burner power to maintain a gentle rolling boil rather than a violent one. A partially covered kettle reduces evaporation but risks DMS issues. Electric kettles with controlled wattage give consistent, lower boil-off rates.

BrewCalcs

Boil-Off Rate Calculator

Calculate your system's boil-off rate from pre and post boil volumes.

Pre-Boil Volume

Volume at the start of the boil

Post-Boil Volume

Volume at the end of the boil

Boil Duration

Total boil time (usually 60 or 90 min)

Kettle Diameter

Internal diameter of your brew kettle

How We Calculate This

The calculator determines your system-specific boil-off rate from measured pre-boil and post-boil volumes.

Formulas

Total boil-off = Pre-boil volume - Post-boil volume
Boil-off rate = Total boil-off / Boil duration (hours)
Boil-off % = (Total boil-off / Pre-boil volume) x 100

Typical ranges: 10-15% for electric systems, 12-18% for gas. Record over several brews for a reliable system profile.

Frequently Asked Questions

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Last updated: March 2026

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