Enter your observed (experimental) value and the true (accepted) value to calculate the percent error. Everything runs in your browser — nothing you enter here is uploaded, stored, or logged.
Calculated locally in your browser — nothing is sent to our server.
How This Calculation Works
Percent error measures how far an observed or measured value is from a known true or accepted value, as a percentage: |observed − true| ÷ |true| × 100. It’s commonly used in science experiments to express how accurate a measurement was. The true value cannot be zero, since that would require dividing by zero.
FAQ
Can percent error be negative?
This calculator always shows the absolute (unsigned) percent error, since the direction of the error (too high or too low) usually matters less than its size.
Is my data uploaded anywhere?
No. The calculation happens entirely in your browser using JavaScript.