Proofing calculator: how much water to add to spirit

Enter how much spirit you have, its strength and the strength you want, for the water to add, the volume it makes and how many bottles that fills.

How it works

The alcohol stays the same when you add water; only the volume around it grows. So the final volume is the volume now × the strength now ÷ the target, and the water is the difference.

final volume = volume × strength now ÷ target

water = final volume − volume

Use the true strength, corrected for temperature: warm spirit reads high, and a strength a degree or two out shifts the water noticeably. The alcoholmeter calculator corrects it.

Worked examples

• 2 L at 65% taken to 40%: 2 × 65 ÷ 40 = 3.25 L in all, so 1.25 L of water. That fills four 70 cl bottles with 450 mL over.
• 1 US gallon at 120 proof taken to 80 proof: 1 × 120 ÷ 80 = 1.5 gallons, so half a gallon of water.

Good to know

• Alcohol and water shrink a little when mixed, so this much water leaves the spirit a few tenths over target. Add about nine tenths of it, let it settle, measure, then add the rest slowly.
• Mixing warms the spirit. Let it cool to 20 °C and rest before the final reading.
• Use distilled, deionised or reverse-osmosis water. The minerals in tap water can cloud spirit or leave a sediment.