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How do I convert 91% rubbing alcohol to 70% rubbing alcohol?

Updated February 21, 2017

Rubbing alcohol is a solution of isopropyl alcohol in water. Ninety-one per cent rubbing alcohol contains 91 per cent isopropyl alcohol as measured by volume and is useful for a wide variety of tasks and chores around the home, including first aid, cleaning and disinfecting surfaces. In general, it's not necessary to dilute 91 per cent rubbing alcohol before using it, but if you need a weaker solution of rubbing alcohol to clean a particular item, follow the steps outlined below.

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  1. Measure out one cup of 91 per cent rubbing alcohol, and pour it into the plastic container.

  2. Add one-third of a cup of water and stir to mix the solution. The solution is now 70 per cent rubbing alcohol.

  3. Repeat this procedure as often as needed to obtain the desired amount of 70 per cent rubbing alcohol.

  4. Tip

    You can use any amount of rubbing alcohol you like as long as the combined volume of the water you add and the 91 per cent rubbing alcohol is equal to 1.3 times the volume of the 91 per cent rubbing alcohol alone.


    Do not drink or ingest rubbing alcohol or any kind of isopropyl alcohol, no matter how dilute the solution. According to the JT Baker material safety data sheet, the lethal dose of isopropyl alcohol for an adult human can be as little as eight oz. If you think you have inadvertently ingested isopropyl alcohol, seek medical attention immediately.

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Things You'll Need

  • Water
  • Plastic container
  • Measuring cup
  • 91 per cent rubbing alcohol
  • Spoon

About the Author

Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.

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