You Want to Dilute Your Whiskey but Don't Know How Much Water to Add
A bottle of cask-strength whiskey is 130 proof (65% ABV). You want to bring it down to 90 proof for easier sipping. Or you're making a cocktail and need to calculate exactly how much water to add to achieve your target strength. Getting this calculation wrong leaves you with something too weak or too strong, and there's no going back.
What This Calculator Does
This alcohol dilution calculator tells you exactly how much water to add to any spirit to reach your target proof or ABV. You input the starting proof or ABV, the volume of spirit you have, and your target proof or ABV. The calculator shows how much water to add and the final total volume. Whether you're proofing down a bottle for personal use or creating a consistent cocktail recipe, this calculator removes the guesswork.
How to Use This Calculator
Start by identifying your starting spirit's ABV (alcohol by volume) or proof. This is on the bottle's label, typically listed as a percentage (ABV) or as "proof," which is double the ABV. A 100-proof spirit is 50% ABV.
Enter the amount of spirit you have (in milliliters or ounces). Then enter your target ABV or proof, the strength you want to achieve. The calculator displays how much water to add and your resulting total volume.
For example: You have 750 mL of 120-proof whiskey (60% ABV) and want to dilute it to 100 proof (50% ABV).
The Formula Behind the Math
Alcohol dilution uses the Pearson Square method, also called alligation. It calculates how much water dilutes a spirit to a target strength.
The basic formula:
Final volume = (Initial ABV × Initial volume) ÷ Target ABV
Water to add = Final volume − Initial volume
Let's work through a concrete example. You have 750 mL of 130-proof whiskey (65% ABV) and want 100 proof (50% ABV).
Your result: 975 mL of 100-proof whiskey made from 750 mL of 130-proof whiskey plus 225 mL of water.
Quick reference for common proof conversions:
The principle is straightforward: the amount of pure alcohol never changes, you're only adding water. Once you understand that 750 mL of 65% ABV spirit contains a fixed amount of pure alcohol (487.5 mL), you can dilute that alcohol to any target strength by dividing its volume by your target percentage and calculating how much water gets you there.
Our calculator does all of this instantly, but now you understand exactly what it's computing.
Proof vs. ABV: What's the Difference?
In the United States, proof is double the ABV. A spirit that's 50% alcohol by volume is 100 proof. This system comes from historical alcohol measurement but persists today.
Common proof levels:
Outside the US, most countries use ABV exclusively. A bottle labeled 40% is 40% alcohol by volume.
Why Distillers Dilute Spirits
Commercial distilleries dilute spirits before bottling because:
Dilution for Cocktail Making and Water-Down Spirits
If you're making cocktails, you might add water to control ABV and improve mouthfeel. A spirit-forward cocktail uses less water; a refreshing drink uses more.
For a classic cocktail recipe that specifies proof (like classic recipes that assume 80-proof bourbon), if you use higher-proof bourbon, you're changing the drink's strength. Some bartenders dilute high-proof spirits to 80 proof before making cocktails to maintain consistency with traditional recipes.
For spirits you're keeping at home, dilution is personal preference. Many whiskey enthusiasts add a small amount of water to open up the spirit's aromas and reduce the burn of high alcohol, revealing more complex flavors.
Water Chemistry and Mineral Content
The water you use for dilution matters subtly. Distilled water is pure but lacks minerals that give water mouthfeel. Filtered tap water works fine for most purposes. Mineral water adds a slight mineral taste that some people prefer. For spirits you're keeping long-term, any clean water works, the spirits' ABV prevents spoilage.
Tips and Things to Watch Out For
Add water to spirits, not spirits to water. This is an old chemistry rule, but for dilution purposes, the order doesn't matter chemically. However, some bartenders believe adding spirit to water distributes flavors better. For home use, the difference is negligible.
Mix gently and let it sit. After dilution, stir or shake gently and let the spirit sit for at least 24 hours before tasting. Flavors integrate better after a day.
Chill if desired. Dilution is sometimes done at cold temperatures to slow the process and cool the spirits. Cold spirits are denser, which affects calculation slightly, but not enough to matter for home use.
Measure precisely. For consistent results, use milliliters or a graduated measure, not eyeballing. A kitchen scale that measures liquid (in grams, where 1g of water ≈ 1 mL) works too.
Document what you do. If you dilute a bottle successfully, note the exact amounts so you can replicate it or use the information if sharing the bottle.
Don't waste high-proof spirits. If you're proofing down, ensure you're starting with a spirit worth diluting, you're still keeping it at that lower proof permanently. Don't dilute a $200 cask-strength bottle if you didn't want cask-strength in the first place.
Frequently Asked Questions
Can I dilute all spirits the same way?
Yes, the math is identical. Whether you're diluting whiskey, rum, vodka, gin, or tequila, the calculation is the same. Flavor impacts vary (water might mellow a spicy spirit more noticeably than a smooth one), but the math doesn't change.
What if I want 90 proof but can only find 80-proof or 100-proof spirits?
You can't dilute an 80-proof spirit to 90 proof, dilution only reduces strength. You'd need to mix 80-proof with 100-proof spirits in the right proportions, which is more complex. It's easier to buy the proof you want.
Does the order of adding water affect the result?
No. Adding water to spirit or spirit to water gives the same final ABV. However, some sources recommend adding water slowly to spirits, or stirring after mixing, to ensure even distribution.
Can I dilute spirits and age them?
Yes. Some spirits improve with a few months of aging after dilution, as flavors integrate. Others (like vodka) won't change noticeably. Scotch whisky typically isn't re-aged after bottling, but home distillers sometimes dilute and age for personal use.
How accurate does the calculation need to be?
For personal drinking or casual mixing, within 1–2 proof is fine. For consistent cocktail recipes or commercial purposes, precision to 0.5 proof matters. Use a graduated cylinder or scale for better accuracy than eyeballing.
What happens if I accidentally dilute too much?
You've created a lower-proof spirit. You can't easily remove water to raise the proof. You can mix it with higher-proof spirit, but you'd need to calculate that new mixture's ABV.
Related Calculators
Use our measurement converter to convert between milliliters, ounces, and other volume units. Our recipe scaling calculator is useful if you're scaling a cocktail recipe. The volume converter helps with volume unit conversions.