Dilution & Concentration Calculator
Hit your target gravity every time. Calculate how much water to add or how long to boil to adjust your wort strength.
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How Dilution and Concentration Work
The gravity of wort is determined by the amount of dissolved sugars per unit volume. If you change the volume without adding or removing sugar, the gravity changes proportionally.
Diluting (Adding Water)
Adding water increases volume while keeping total sugar constant. The gravity drops because the same sugar is spread across more liquid. The formula is:
Water to add = volume x ((current_gravity - 1) / (target_gravity - 1) - 1)This works because gravity points (the digits after 1.0) are proportional to sugar concentration. If you have 25 litres at 1.060 and want 1.050, you need about 5 litres of water.
Concentrating (Boiling Down)
Boiling evaporates water, reducing volume while keeping total sugar constant. The gravity rises because the same sugar is now in less liquid.
Target volume = volume x (current_gravity - 1) / (target_gravity - 1)The boil time depends on your system's boil-off rate — how many litres of water evaporate per hour. A typical homebrew system loses 3-5 litres per hour. The calculator divides the volume to remove by this rate to estimate the boil time.
When to Use This
- Your pre-boil gravity is higher than expected — dilute with water before or during the boil to hit your target OG.
- Your pre-boil gravity is lower than expected — extend the boil to concentrate the wort and raise the gravity.
- High-gravity brewing — brew a concentrated wort intentionally and dilute to serving strength before or after fermentation.
Frequently Asked Questions
How do I dilute wort to a lower gravity?
Add water. The formula calculates exactly how much based on your current volume and gravity. For example, if you have 20 litres at 1.060 and want 1.050, you need about 4 litres of water.
How do I increase the gravity of my wort?
Boil it down. Evaporating water concentrates the sugars, raising the gravity. The amount of time depends on your boil-off rate (typically 3-5 litres per hour). Switch to "Concentrate" mode in the calculator to see the exact boil time.
What is a typical boil-off rate?
Most homebrew systems boil off between 3 and 5 litres per hour. The default in our calculator is 3.8 L/hr. Your actual rate depends on your kettle diameter, burner power, and whether you boil with the lid on or off. Measure yours by noting the volume before and after a timed boil.
Should I dilute before or after fermentation?
It depends on your goal. Diluting pre-fermentation (in the kettle) is the most common approach and lets yeast work with the final gravity from the start. Diluting post-fermentation is sometimes done for high-gravity brewing, where you brew a strong wort and dilute to serving strength. Both work, but pre-fermentation is simpler.
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