Measure your wash or must with a hydrometer before and after fermentation – the calculator works out the ABV of your wine, beer or wash and how much distillate you will get from it.
Wash strength and distillation yield
Knowing the strength and volume of the wash, the calculator works out the amount of pure alcohol and the expected yield of 40% and 96% distillate at about 90% distillation efficiency. This lets you judge whether fermentation went well before you fill the still.
How do I measure OG and FG?
Measure OG (original gravity) after all the sugar has dissolved, before adding yeast. Measure FG (final gravity) when fermentation has finished and the reading has not changed for 2–3 days. Degas the sample, as CO₂ bubbles push the hydrometer up.
How we calculate
ABV = 76.08 × (OG − FG) / (1.775 − OG) × FG / 0.794 (more accurate than the classic 131.25 × ΔSG for strong washes). Blg is converted to SG with the ASBC formula.
Frequently asked questions
Why does the hydrometer read below zero?
Alcohol is lighter than water, so a fully fermented wash has a density below 1.000 – a good sign that the sugar is used up.
How do I know fermentation has finished?
The hydrometer reading stays the same for 2–3 days, the airlock stops bubbling and the wash starts to clear. Then measure the FG and calculate the strength.
Which hydrometer should I choose?
For washes the best is a hydrometer with a −5 to +25°Blg scale, which also shows readings below zero after full fermentation.
Can I tell the strength from the final gravity alone?
No. You need a reading before fermentation, because the strength depends on how much sugar the yeast has converted into alcohol.