Convert a percent to a decimal by dividing by 100, or turn a decimal back into a percent, with the matching fraction, per-mille and ppm shown too.
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Percent to Decimal Formula
The calculator uses one of two formulas depending on the direction you choose.
To turn a percent into a decimal, divide the percent by 100:
decimal = percent / 100
To turn a decimal back into a percent, multiply the decimal by 100:
percent = decimal * 100
- percent: the value written with a percent sign, such as 45%
- decimal: the same value written as a plain number, such as 0.45
- 100: the constant that comes from "percent" meaning "per hundred"
The "I want to convert" selector sets which formula runs. In Percent to Decimal mode you enter the percent and the calculator divides by 100, which is the same as moving the decimal point two places to the left. In Decimal to Percent mode you enter the decimal and the calculator multiplies by 100, moving the point two places to the right. An optional rounding field sets the number of decimal places, and every result also shows the value as a reduced fraction, in parts per million (ppm), and in per-mille, where 1 percent equals 10 per-mille.
Common Percent and Decimal Equivalents
These conversions cover the values you will meet most often.
| Percent | Decimal |
|---|---|
| 1% | 0.01 |
| 5% | 0.05 |
| 10% | 0.1 |
| 25% | 0.25 |
| 50% | 0.5 |
| 75% | 0.75 |
| 100% | 1 |
| 150% | 1.5 |
| 0.5% | 0.005 |
The next table shows how the same value looks in the extra formats the calculator also displays.
| Percent | Decimal | Per-mille | ppm |
|---|---|---|---|
| 1% | 0.01 | 10 | 10,000 |
| 5% | 0.05 | 50 | 50,000 |
| 0.1% | 0.001 | 1 | 1,000 |
Example Problems
Example 1: Convert 45% to a decimal. Divide the percent by 100, so 45 / 100 = 0.45. You get the same answer by moving the decimal point in 45 two places to the left.
Example 2: Convert 0.085 to a percent. Multiply the decimal by 100, so 0.085 * 100 = 8.5%. Moving the decimal point in 0.085 two places to the right gives the same 8.5%.
Frequently Asked Questions
How do you convert a percent to a decimal? Divide the percent by 100 and drop the percent sign. For example, 30% becomes 30 / 100 = 0.3. A quick shortcut is to move the decimal point two places to the left, so 30% turns into 0.30, which is the same as 0.3.
How do you change a decimal back into a percent? Multiply the decimal by 100 and add a percent sign, or move the decimal point two places to the right. For example, 0.6 becomes 0.6 * 100 = 60%, and 1.25 becomes 125%. Use the Decimal to Percent mode to do this automatically.
What do the ppm and per-mille outputs mean? They are two more ways to write the same fraction of a whole. Per-mille is parts per thousand, so 1 percent equals 10 per-mille. Parts per million (ppm) is parts per million, so 1 percent equals 10,000 ppm. These units are common in chemistry, water testing, and finance, where the values are very small and a plain percent would have many leading zeros.
