# How to Calculate Relative Error

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To calculate relative error, divide the experimental value by the real value and then divide that number by the real number to get a percentage of relative error. Calculate relative error, often used for science experiments, with advice from a standardized test prep instructor in this free video on mathematics.

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## Video Transcript

Let's take a look at relative error. My mission in this one minute clip is to make you really understand this. Rather than to just memorize the formula. Because it actually makes a lot of sense. A lot of times, people are intimidated by the formula. But you'll see, it makes a lot of sense. So let's say, you're in Science class. And you've done a lab. You're supposed to calculate the weight of something. And you know, you in your lab, you've got to do with six grams. And maybe you know, that it's supposed to have been five grams. In the lab, they'll very often ask you to calculate the, exper the relative error. Or sometimes they call it experimental error. So here's the formula. Let's look at that first. So experimental means, how much did you get in your experiment? That's all it means. So your experimental was 6. And then minus the real. What was the real? The real was 5. We know that's what it was supposed to be. And then divide it by real. So 6 minus 5 is 1. Over 5. Which is point 2 (.2) or 20 %. That tells us that the relative error was 20%. You were 20% off, from the real number. So how does the formula work? The formula is just what you got. Minus what it's supposed to be. So that's what your error. That's called the absolute error. It's just, how much were you off. You know. Divide it by real. Because it says, how much were you off? Out of the whole thing. Like you were off, one gram. If this weighed a million grams and you were off one gram. That'd be nothing. So the relative error would be very, very small. But one gram out of six grams, out of five grams, I mean. Is a fair bit. That's why it's called relative error. It's relative to how much it really weighed. So we did the absolute error. How much were you off? But then, divide it by the real thing. How much were you off? Out of the total. And that's why it's called relative error. And that's why the formula really makes sense. Just how much were you off, out of the whole thing?

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