Merry Cuss Brew Club

Water Addition For Decreasing Gravity


This calculator is for decreasing the gravity of your wort by adding water.

Data Entry

Measured Volume (in gallons)

Measured Specific Gravity

Target Specific Gravity


Gallons of water to add (boil off) to reach the target gravity:


This calculator determines the amount of water needed to lower the gravity of a wort to a given target. For example, if the original gravity is a bit higher than your target, this will determine the amount of additional water that is needed to reach the target gravity. If your actual gravity is a bit lower than the target, the result will be a negative number showing the gallons that need to be boiled off to reach the target gravity.

The calculator begins by determining the difference between the actual gravity and target gravity. This difference is then used to determine the amount of water needed. For example, let's say that you were aiming to brew 5.0 gallons of a 1.050 wort, but ended up with a wort of 1.055. This means that each gallon has five extra gravity points. Altogether, there are 25 extra gravity points (5 points per gallon * 5 gallons). These 25 points will be enough to make a half gallon of wort at 1.050. Adding a half gallon of water will yield 5.5 gallons of 1.050 wort.

A good strategy for all-grain brewing is to aim for slightly more gravity than the target gravity. The wort can then be easily thinned with water to get the desired target gravity.

For further information, please refer to chapter 6 of Daniels (2001) on "Hitting Target Gravity".


Daniels, R. (2001). Designing Great Beers. Brewers Publications. Boulder, Colorado.

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