A lot of people get confused by the “%” symbol. I can understand why. Even the Wikipedia Percentage page seems way more confusing than it should be.

Well, maybe I can help.

Here’s a simplifying little idea that I learned by reading ISO 80000-1:

The percent symbol (%) is just a constant, just like

πore. Its value is 0.01 (or 1/100, if you prefer).

Let me show it to you in a table. Maybe that’ll clear it up:

What this means is that anywhere you see the “%” symbol, you’re free to substitute the value 0.01:

50% = 50(0.01) = 0.5

So, how does that help? Well, it gives you a simple rule you can apply instead of having to intuit how to convert something to or from a percentage.

For example, I used to find myself wondering, “If I want to convert this percentage to a real number, do I multiply by 100? Or divide?” I hate memorizing crap like that.

But knowing that % = 0.01 makes it easy. For example, converting 42% to a number without the % sign, I simply substitute, like this:

42% = 42(0.01) = 0.42

When you know that % = 0.01, it’s easy to see that 100% is just another way of expressing the number 1:

100% = 100(0.01) = 1

Converting a number *to* a percentage is easy, too. I can of course multiply anything I want by 100% and still have the same quantity I started with. Here’s how to convert 0.0005 to a percentage:

0.0005 = 0.0005 × 1

= 0.0005 × 100%

= (0.0005 × 100)%

= 0.05%

Yep, ISO 80000-1… I don’t do everything it says, but this percentage thing was a nice revelation.

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