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Alcohol Dilution Calculator

Dilute IPA or ethanol to a target % v/v and the water to add.

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Alcohol dilution calculator

V₁ × C₁ = V₂ × C₂ (v/v %) — dilute IPA or ethanol to a target strength.

% v/v

Typical stocks: 99% (IPA), 95% (ethanol), 100% (absolute).

% v/v

e.g. 70% for surface disinfection.

mL

Quick presets

Stock alcohol to measure
70.71mL
Water to add (ideal)29.29 mL
Final volume100 mL
Volumes assume ideal mixing. Ethanol–water mixtures contract on mixing, so the calculated water volume is a slight over-estimate; measure the final volume against a graduated vessel and top up if needed.

Formula and how to use it

Alcohol strength labelled as % v/v is diluted with the same conservation equation used for any solution: V₁ × C₁ = V₂ × C₂, where V₁ is the volume of stock alcohol, C₁ its strength, V₂ the final volume, and C₂ the target strength.

To make 100 mL of 70% from 99% IPA: V₁ = (70 × 100) / 99 = 70.7 mL of stock, made up to 100 mL with distilled water. Real ethanol–water and IPA–water mixtures contract on mixing, so the ideal calculation slightly overestimates the water needed; always make up to the final volume in a graduated cylinder rather than blindly adding the computed water volume.

This calculator solves V₁ and the water to add for any stock strength, target strength, and final volume, with presets for the most common laboratory dilutions (99% → 70%, 95% → 70%).

Alcohol Dilution Calculator — FAQ