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Wort dilution is a practical technique every all-grain homebrewer uses at some point, you hit a higher-than-expected original gravity and need to add water to bring it into the target range, or you end up with less pre-boil volume than planned and need to recalculate your expected OG. Understanding dilution math lets you make these adjustments confidently mid-brew rather than guessing or accepting a batch that’s off-target. The formula is simple and the calculator handles the arithmetic instantly.
The dilution formula
Dilution follows the basic concentration equation: initial volume × initial gravity = final volume × final gravity. Rearranged to solve for the water needed to dilute a high-gravity wort to a target gravity:
Water to add = Current Volume × ((Current Gravity − Target Gravity) / Target Gravity)
Or equivalently:
Final Volume = Current Volume × (Current Gravity / Target Gravity)Where gravity values use the gravity points format (e.g., 1.065 OG = 65 gravity points). This approach is especially clean: if you have 5.5 gallons at 1.072 and want 1.065, you need 5.5 × (72/65) = 6.09 gallons final volume, meaning add approximately 0.6 gallons of water.
Dilution & Gravity Calculator
[dilution_calculator]
When dilution is appropriate
High mash efficiency. If your system consistently overshoots OG, dilution at the end of the boil is a clean fix. Add water, stir thoroughly, then take a final gravity reading. Always add water before pitching yeast, never after fermentation has started.
Top-up water for extract brewing. Partial boil extract brewers routinely dilute concentrated wort with cold water in the fermenter to reach full batch volume. Stir vigorously to ensure complete mixing before taking the OG reading, stratified wort (warm concentrated wort layered over cold water) gives false gravity readings.
Blending batches. Dilution math applies when blending a high-gravity beer with a low-gravity one to hit a target, same formula, just with two volumes rather than one volume and pure water. Use the mixing equation: (V1 × G1 + V2 × G2) / (V1 + V2) = Blended Gravity.
Common Questions
Does adding water affect anything besides gravity?
Yes. Diluting wort reduces IBU concentration proportionally (same amount of iso-alpha acids in a larger volume = fewer IBUs per volume), reduces hop aroma intensity, and dilutes color (lower SRM). If your IBU calculation was based on the original smaller volume, your beer will be slightly less bitter than calculated after dilution. For small dilutions (under 10% volume increase), the effect on color and bitterness is minor. For larger dilutions, recalculate IBUs and SRM using the final volume. Dilution also reduces any off-flavors if present in the original wort, occasionally useful when a boil-off calculation went wrong and the wort tastes harsh from concentration.
Can I use tap water for dilution, or does it need to be treated?
Ideally, use water of the same quality as your brewing water, pre-treated tap water (dechlorinated or filtered to remove chloramine) or RO water. Adding untreated chloraminated tap water to finished wort introduces chloramine that can react with phenolic compounds in the beer to form chlorophenols, producing a medicinal or plastic off-flavor. If you need to add tap water post-boil, add a Campden tablet (potassium metabisulfite, 1/4 tablet per 10 gallons) to neutralize chloramine in the dilution water before it contacts the wort.
