Beer Dilution and Boil-Off Calculator
Created by: Natalie Reed
Last updated:
Forecast gravity concentration from boil-off and compute dilution adjustments to hit target wort specs.
Beer Dilution and Boil-Off Calculator
HomebrewingPlan gravity concentration and dilution adjustments
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What is a Beer Dilution and Boil-Off Calculator?
A dilution and boil-off calculator helps you predict how evaporation changes gravity and how much water to add if gravity drifts away from target. It is useful both during recipe design and as a corrective tool on brew day.
Because concentration changes quickly as boil volume drops, even small errors in boil-off assumptions can impact final OG and ABV. This tool converts those relationships into clear volume and gravity decisions.
Gravity-Volume Conservation Formula
Points × Volume is conserved: (GP₁×V₁) = (GP₂×V₂)
Gravity points are calculated as $(SG-1)\times1000$. During concentration and dilution, total points remain constant while volume changes.
The same relationship can estimate post-boil gravity, required dilution water, and pre-boil volume targets for a desired final batch size.
Example Brew-Day Correction
If boil-off is higher than expected, post-boil volume will be lower and gravity will rise. You can use this calculator to estimate exactly how much sterile water is needed to bring wort back to your target gravity.
Likewise, if gravity is too low, the tool helps you understand whether longer boil concentration or recipe changes are better options for that batch.
Common Applications
Use this calculator for pre-boil planning, post-boil corrections, and equipment profiling. It is especially useful when changing kettle geometry, burner intensity, or batch size.
Consistent gravity control improves style accuracy and makes downstream fermentation planning more predictable.
Accuracy Tips
Measure your real boil-off rate under normal brewing conditions and refresh it seasonally if ambient conditions vary.
When diluting, use sanitized, low-oxygen water to protect flavor stability and reduce contamination risk.
Frequently Asked Questions
What does this calculator do?
It predicts how boil evaporation changes volume and gravity, then estimates dilution water needed to return to a chosen gravity target. This supports both proactive planning and mid-process correction. It is especially useful when actual boil-off differs from assumptions and you need a controlled, math-based adjustment path.
What are gravity points?
Gravity points are calculated as $(SG-1) imes1000$ and represent dissolved extract concentration in practical brewing units. During concentration or dilution, total points are conserved when accounting for volume. This conservation principle is the basis for reliable gravity correction calculations before and after boil.
Why is boil-off rate important?
Boil-off directly changes kettle volume, which changes concentration and therefore gravity. If actual evaporation is higher than expected, gravity rises and finished volume drops. If lower, gravity may finish under target. Tracking real boil-off on your system is one of the most important steps for predictable OG and batch yield control.
Should I dilute before or after boil?
That depends on process goals. Pre-boil adjustments can smooth concentration trajectory, while post-boil dilution is common when gravity finishes high. Either way, use sanitary, low-oxygen water and recalculate after each significant adjustment. Controlled incremental corrections usually produce better outcomes than one large unverified change.
Can this help with extract brewing top-off planning?
Yes. The same gravity-point conservation logic applies to concentrated boils followed by top-off water additions. By calculating final volume and gravity relationships, you can estimate how much top-off water is needed to hit planned OG. This improves repeatability and reduces surprises in partial-boil or concentrated-wort workflows.
Sources and References
- Palmer, John J. "How to Brew: Everything You Need to Know to Brew Great Beer Every Time." 4th Edition. Brewers Publications, 2017. Detailed coverage of boil-off rates, gravity adjustments, and volume-concentration calculations for homebrewing applications.
- Daniels, Ray. "Designing Great Beers: The Ultimate Guide to Brewing Classic Beer Styles." Brewers Publications, 1996. Analysis of dilution techniques, blending strategies, and gravity management for recipe formulation and correction.
- American Society of Brewing Chemists (ASBC). "Methods of Analysis." Gravity measurement standards, wort concentration techniques, and analytical best practices for brewing operations.