Enter the accepted value and the measured value; the percent error updates as you type.
Percent Error Calculator Online
Enter the accepted (theoretical) value and the measured (experimental) value; the percent error, the absolute error, and whether the measurement ran high or low update as you type.
Use it for a lab measurement against a known reference value, a manufacturing tolerance check, or comparing an estimate against the actual result.
The accepted and measured values stay in the browser - the percent error is computed on this device, with no upload and no account.
What happens at zero and negative values
Type a 0 into the accepted value field and the percent error calculator does not divide by zero or show Infinity or NaN - it shows an inline prompt asking for a non-zero accepted value instead, since percent error is undefined when there is nothing to compare against. Clearing the accepted field entirely has the same effect, because a blank field is treated as 0 the same way a typed 0 is.
The accepted value can be negative too - useful for a lab measurement that runs below zero, like a temperature reading. With an accepted value of -50 and a measured value of -45, the calculator reports a 10% percent error and an absolute error of 5, matching a positive-value comparison of the same size. One quirk worth knowing: the high or low direction label compares the two numbers directly (-45 is higher than -50, so it reads "high"), while the signed error percentage divides by the accepted value, so a negative accepted value can flip the sign of that percentage relative to the direction label - here the signed error prints -10% even though the direction says high.
Percent error is not capped at 100% either. If the measured value is far enough from the accepted value - including landing on a completely different sign - the percent error can read well over 100%, because the formula compares the size of the gap to the size of the accepted value rather than to a fixed scale. An accepted value of 50 against a measured value of -10, for example, reports a 120% percent error and an absolute error of 60.
Frequently Asked Questions
What does Percent Error Calculator Online do?
Enter the accepted (theoretical) value and the measured (experimental) value and it works out the percent error, the absolute error, and whether the measured value ran high or low.
When should I reach for percent error calculator online?
Use it for a lab measurement against a known reference value, a manufacturing tolerance check, or comparing an estimate against the actual result.
What complementary tools work well alongside percent error calculator online?
Looking for a plain percentage instead - X% of Y, what percent one number is of another, or a percent change? Use the percentage calculator for that; this tool is specifically for comparing a measured value against an accepted value.
What happens if I clear the measured value field?
An empty measured-value field is treated as 0, the same as if you had typed 0 - so clearing it while the accepted value stays at its default of 100 shows a 100% percent error rather than leaving the previous result on screen.
Does the calculator show anything different when the two values match exactly?
Yes - when the measured value equals the accepted value, the percent error and absolute error both read 0 and the direction label reads exact instead of high or low.
How many decimal places does the result use?
Percent error and signed error are shown to up to 4 decimal places and absolute error to up to 6, with trailing zeros trimmed automatically - a clean 2% result displays as 2%, not 2.0000%.
Can I enter decimal values instead of whole numbers?
Yes - both the accepted value and the measured value accept any decimal number, not just whole numbers, so a measurement like 98.5 works the same as a whole number like 98.
Does the calculator format numbers differently depending on my language settings?
The result numbers follow your browser's own locale formatting, so the decimal separator can look different from one visitor to the next - some locales show a comma instead of a period, for example - while the underlying percent error, absolute error, and signed error values stay the same.
Does the calculator start with example numbers already filled in?
Yes - it loads with an accepted value of 100 and a measured value of 98 already filled in, giving a 2% percent error right away, so you can see how the output looks before typing your own numbers.