How to calculate percentage strength given ratio strength

Updated February 21, 2017

A ratio is a comparison between to values. For example, a solution containing 9 units of salt in 100 units of water has a ratio of 9:100, and a solution of 30 units of alcohol in 100 units of water has an alcohol to water ratio of 30:100. Percentages are also ratios, when the values are expressed out of a total of 100. The term "percent" literally means "per one hundred." Converting from ratio strength to percentage strength is straightforward, but a calculator is required.

Reduce the strength ratio to the lowest common denominator. For example 10:200 can be reduced to 1:20.

Divide 100 by the second number in the ratio. The result is the percentage value of each unit in the solution.

For example the ratio 1:20, contains 20 units. The percentage value of each unit is 100 / 20, or 5.

Multiply the first number in the ratio by the result from Step 2. The result is the strength of the solution expressed as a percentage.

For example, the percentage strength of a 1:20 ratio is 5 per cent because 1 x 5 = 5.


Use an online ratio to percentage calculator to simplify the process. The percentage strength of a solution is the same is the number of grams per 100ml.

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About the Author

David Robinson has written professionally since 2000. He is a Fellow of the Royal Geographical Society and the Royal Meteorological Society. He has written for the "Telegraph" and "Guardian" newspapers in the U.K., government publications, websites, magazines and school textbooks. He holds an honors Bachelor of Arts in geography and education and a teaching certificate from Durham University, England.