🎯 Percent Error Calculator
Compare a measured value to the accepted value: percent error = |experimental − theoretical| ÷ |theoretical| × 100.
Percent error
0.101937%
Signed error
-0.101937%
measured low
Percent error = |experimental − theoretical| ÷ |theoretical| × 100. 🔒 Computed in your browser.
How the percent error calculator works
Percent error measures how far a measurement is from the accepted value: |experimental − theoretical| ÷ |theoretical| × 100. The tool also shows the signed error, (experimental − theoretical) ÷ |theoretical| × 100, which keeps the sign: a positive result means your measurement overshot the accepted value, a negative one that it fell short.
The standard lab metric for accuracy. A small percent error means your measurement is close to the accepted value; the signed version tells you the direction of the discrepancy.
Frequently asked questions
How do you calculate percent error?
Take the absolute difference between the experimental and theoretical values, divide by the absolute theoretical value, and multiply by 100: |exp − theo| / |theo| × 100.
What is a good percent error?
It depends on the experiment, but in student labs under about 5% is often considered good. Lower is better; the acceptable range depends on the equipment and method.
What is the difference between percent error and percent difference?
Percent error compares a measurement to a known accepted value; percent difference compares two measured values with no “correct” reference (dividing by their average).
Can percent error be negative?
The standard percent error uses absolute value, so it is non-negative. This tool also shows a signed error to indicate whether the measurement was too high (+) or too low (−).
Why divide by the theoretical value?
Because the theoretical (accepted) value is the reference standard; the error is expressed relative to it, making it comparable across different scales.
A measurement gives 9.6 g/mL but the accepted value is 10.5, what is the percent error?
|9.6 − 10.5| ÷ 10.5 × 100 = 8.6%. The signed error is −8.6%, showing the measurement came out low.
What causes percent error in an experiment?
Systematic errors (a miscalibrated instrument, a consistent reading bias) and random errors (fluctuations you can average out). Percent error captures the combined gap between your result and the accepted value.
How can I reduce percent error?
Calibrate instruments, repeat measurements and average them, control conditions like temperature, and use appropriate significant figures. A smaller percent error means better accuracy relative to the accepted value.
What is the difference between percent error and standard deviation?
Percent error measures accuracy, how close a result is to the accepted value. Standard deviation measures precision, how tightly repeated measurements cluster together. A set of readings can be precise (low spread) yet inaccurate (high percent error).
What if I don’t have an accepted value to compare against?
Then percent error does not apply, because it needs a known reference. Compare two experimental values with percent difference instead, dividing their absolute difference by their average.