Math
Percent Error Calculator
Use this percent error calculator for chemistry, physics, and lab reports when you need to compare a measured value with an accepted or theoretical value.
The measured or observed value.
The true, expected, or reference value.
Percent error
—
- Absolute error
- —
- Signed error
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the percent error calculator solves
Use this percent error calculator for chemistry, physics, and lab reports when you need to compare a measured value with an accepted or theoretical value.
Formula
How to use it
- Enter the measured value from the experiment.
- Enter the accepted or theoretical value.
- Read the percent error and the raw error difference.
How to read the answer
A smaller percent error means the measurement is closer to the accepted value. The signed error tells you whether the measurement was high or low.
Common mistakes and edge cases
- Do not divide by the experimental value unless your teacher specifically asks for percent difference.
- The accepted value cannot be zero in the usual percent error formula.
- Use absolute value for percent error, but keep signed error when direction matters.
Worked examples
Lab value slightly low
Percent error
2%
Measured value high
Percent error
4%
Frequently asked questions
Can percent error be negative?+
Percent error is usually reported as a nonnegative percentage because it uses absolute error. The signed error can be negative when the measured value is low.
What is a good percent error?+
It depends on the experiment. In many classroom labs, a lower percent error is better, but the expected tolerance depends on equipment and method.
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Last updated: May 8, 2026