This percent error calculator tells you how far a measured or experimental value is from the true or accepted value, expressed as a percentage. It is one of the most common calculations in science classes and laboratories, because it puts the size of an error in context. An error of 2 grams means very little on its own, but as a percentage of the true value it tells you whether a measurement is excellent or wildly off. You enter the value you measured and the value you were aiming for, and the calculator returns the percent error along with the plain absolute error, which is simply the difference between the two. The percent error uses the absolute size of the difference, so it is always reported as a positive number, while the signed difference shown alongside it tells you whether your measurement came in high or low. This is helpful for physics and chemistry experiments, calibrating instruments, checking the accuracy of a forecast or estimate, and comparing a result against a known standard. As a rule of thumb a smaller percent error is better, since it means your measured value sits closer to the true value. Enter your two numbers to see the result update instantly.
The calculator subtracts the true value from the measured value to get the signed difference, takes its absolute size for the absolute error, then divides that by the true value and multiplies by 100 to give the percent error. Dividing by the true value, not the measured value, is the standard convention.
If you measured the acceleration due to gravity as 9.6 and the accepted value is 9.8, the absolute error is 0.2. Divided by 9.8 and multiplied by 100, that is a percent error of about 2.04 percent, with the measurement reading slightly low.
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