How to Calculate Percent

Calculating percent is a fundamental math skill, whether you're taking a class or just living life! Percentages are used to make car and house payments, calculate tips and pay taxes on goods. Percent calculations are fundamental to many classes, especially science courses. Here's a step-by-step tutorial on how to calculate percent.

What Is Percent?

Percentage or percent means 'per one hundred' and expresses the fraction of a number out of 100% or the total amount. A percent sign (%) or the abbreviation "pct" is used to denote percentage.

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Mass Percent Composition Problem

By Anne Marie Helmenstine, Ph.D.

How To Calculate Percent

1. Determine the total or whole amount.
2. Divide the number to be expressed as a percent by the total.
   In most cases, you'll divide the smaller number by the larger number.
3. Multiple the resulting value by 100.

Example Percent Calculation

Say you have 30 marbles. If 12 of them are blue, what percent of the marbles are blue? What percent are not blue?

1. Use the total number of marbles. This is 30.
2. Divide the number of blue marbles into the total: 12/30 = 0.4
3. Multiple this value by 100 to get the percent: 0.4 x 100 = 40% are blue
4. You have two ways to determine what percent are not blue. The easiest is to take the total percent minus the percent that are blue: 100% - 40% = 60% not blue. You could calculate it, just like you did the initial blue marble problem. You know the total number of marbles. The number that is not blue is the total minus the blue marbles: 30 - 12 = 18 non-blue marbles.The percent that is not blue is 18/30 x 100 = 60%
   As a check, you can make sure the total of blue and non-blue marbles adds up to 100%: 40% + 60% = 100%

Learn More

Now that you understand the basic principle, explore practical applications of the percent calculation:

• How to Calculate Mass Percent: Mass percent is used to express the abundance of elements in a sample.
• How to Calculate Percent Composition by Mass
• Percent Error Calculation: Percent error is a common calculation in scientific disciplines.
• Volume Percent Concentration: Aside from mass percent, another common method of expressing concentration is using volume. This is often uses with liquids.