Dilution Calculator
Wort dilution uses the principle that gravity points are conserved when water is added: points × volume stays constant. Given a current gravity and volume and a target gravity, the water needed is V₁ × (OG − 1) / (target − 1) − V₁. The same formula works for topping up a short boil, diluting a parti-gyle first runnings, or adjusting a beer that finished too strong.
Overshot your gravity? This tells you exactly how much water brings it to where you want it.
The formula
Gravity points are conserved when you add water (which has zero points):
final volume = current volume × (OG − 1) / (target gravity − 1)
The water to add is the difference between the final volume and the current volume. A 19 liter batch at 1.080 diluted to 1.050 needs about 11.4 liters of water, bringing the total to 30.4 liters.
When to dilute
- Overshoot in the kettle. A stronger-than-expected wort after the boil is the most common reason. Top up with water to hit your target OG before pitching.
- High gravity brewing. Brew a concentrated wort and dilute post-fermentation to the target ABV. This is standard in commercial brewing and lets you make more beer from less kettle capacity.
- Parti-gyle. The second runnings from a big beer are weaker but still usable. Dilution adjusts them to a target gravity for a session beer.
- Extract brewing with a partial boil. If you boiled a concentrated wort with part of the water, this tells you how much to add to the fermenter to reach your full volume and target gravity.
What else changes
Dilution does not only change gravity. Everything that is dissolved in the wort gets diluted proportionally:
- Bitterness drops by the same factor as gravity. If you dilute by 25%, IBU drops by 25%.
- Color drops, but not linearly — the Morey equation means the visual change is smaller than you expect for pale beers and more noticeable for dark ones.
- Minerals are diluted too. If you treated your water with brewing salts, the concentrations fall with dilution. For large additions, re-calculate your water chemistry.
The brewhouse efficiency calculator can help you diagnose why your gravity came in high in the first place, so you can adjust the recipe for next time instead of diluting again.
Dilution Calculator — questions
Can I dilute after fermentation?
Yes — adding boiled, cooled water to a finished beer lowers the gravity (and ABV) without restarting fermentation. It is a common technique for bringing a too-strong beer into style range, and commercial breweries do it routinely as "high gravity brewing."
Does dilution affect bitterness?
Yes. IBU scales with volume the same way gravity does, so diluting a 19 liter batch to 23 liters reduces both gravity and bitterness by the same proportion. If you are diluting significantly, recalculate your IBU target.
What about parti-gyle brewing?
A parti-gyle splits the runnings into a strong first wort and a weaker second wort. This calculator can tell you how much water to add to the second runnings to hit a target gravity for the smaller beer.
Hit your target gravity the first time
Brewgravity predicts OG from your grain bill and efficiency before you brew — dial in the recipe on screen instead of diluting in the kettle.
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