Most of the time, people use percentages to express a fraction or a portion of a whole. In fact, percent literally means "per 100" or "out of 100." So when you see 25 percent, for example, you could read it as "25 out of 100" or "25 per 100 parts." But you can also have percentages that are greater than 100 percent – and when that happens, there's at least one complete whole, or a whole number, hidden in there somewhere.
TL;DR (Too Long; Didn't Read)
Multiply the whole number by 100. The resulting answer is its value as a percentage. Another way is to add a decimal point after the whole number such as 4, and then move the decimal two spaces to the right, fill in each of those empty spaces with a zero, and add a percentage symbol = 400%.
Converting Decimals Into Percentages
Converting whole numbers into percentages uses the same process as converting decimal numbers into percentages, but the results you get from decimals might be more familiar – so they're a good way to get a feel for the process. Consider 50 percent, which actually means 50 out of 100 or, to write it another way, 50 ÷ 100. If you work out the division, you get the decimal value that represents 50 percent: .5. To convert that decimal back into a percentage, just do the reverse operation, which is multiplying by 100.
Two More Decimal Examples
When you see 30 percent, it means 30 out of 100 or 30 ÷ 100. Work out the division and you have a decimal value that represents the percentage: .3. To convert a decimal value back into a percentage, perform the reverse operation: .3 × 100 = 30 percent. Because percentages always mean "out of 100," you can use the same technique – multiplying by 100 – to turn any number into a percentage. So, if you had .75 multiply it by 100 to get its value as a percentage: 75 percent.
Converting Whole Numbers Into Percentages
This technique also works with whole numbers like 1, 2, 3 and so on. Consider 1: multiply it by 100 to turn it into a percentage, and your answer is 100 percent or "100 out of 100" or, to put it another way, one complete whole. To express the number 2 as a percentage: multiply it by 100 and you'll get a result of 200 percent. This pattern continues for every whole number: Just multiply it by 100 and you'll have your result as a percentage.
What About Decimals Bigger Than One
You can even use this technique for figures that involve both a whole number and a decimal: For example, 4.3. Multiply that by 100 and you have the percentage it represents: 430 percent. If you want to express 3.7 as a percentage, just multiply by 100, which gives you 3.7 × 100 = 370 percent, and so on.
The Not-So-Tricky Zero
Technically, zero is a whole number, which means you can convert it into a percentage. You might intuitively know that zero expressed as a percentage is zero percent, but you can use the same technique to verify it: 0 × 100 does, of course, equal 0 percent.