Percent Error Calculator

You type the value you measured and the true or accepted value, and it works out how far off you were as a percent. It finds the gap between the two, divides by the true value, and multiplies by 100. It also shows the absolute error and whether your measurement came in high or low. Everything runs in your browser, so you'll see the result update as you type, and nothing you enter leaves your device.

Percent error is the size of your mistake measured against the true value. You subtract the true value from your measured value, take the absolute value so the result is positive, divide by the true value, then multiply by 100. So if you measured 9.8 and the true value is 10, the gap is 0.2, and 0.2 divided by 10 is 0.02, which is 2 percent. The calculator runs that the moment you type both numbers.

They answer different questions, so it's worth keeping them apart. Percent error compares a measurement to a known true value, dividing by that true value, which is what you want in a lab or experiment. Percent difference compares two values when neither is the reference, dividing by their average instead. If you have a correct answer to compare against, you want percent error. For two readings of equal standing, use our percent difference tool.

Yes, it can, and that just means your measurement was more than double the true value or far below it. A reading of 25 against a true value of 10 gives a 150 percent error, for example. A small percent error means your measurement is close to correct, while a large one flags a big miss or a mistake in your method. There's no upper limit, though in careful work you'd expect the number to stay low.

Because percent error is about the size of the mistake, not its direction, so it's always reported as a positive number. The absolute value strips off the minus sign you'd get when a measurement lands below the true value. This tool still tells you the direction separately, marking whether you came in high or low, so you don't lose that detail. If you want the signed version, the relative error shown alongside keeps the sign.

Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you enter leaves your device. Type your measured value and the true value, and read the percent error, the absolute error, and the direction in a tap. Bookmark it for lab reports, chemistry and physics homework, or quality checks, and you'll have the formula and the answer in one place whenever you need them.