Compare an experimental or measured value to the accepted (theoretical) value to find how far off it is, as a percentage.
Percent Error Calculator
LivePercent error
4%
Percent error is always shown as a positive value.
The formula
Percent error = |measured - actual| / |actual| x 100
Example
A measured value of 48 against an accepted value of 50: |48-50|/50 x 100 = 4% error.
Step-by-step guide
- Enter your measured (experimental) value.
- Enter the accepted (theoretical or true) value.
- Read the percent error - a smaller number means your measurement was closer to the true value.
Common mistakes
Dividing by the measured value instead of the accepted value - percent error is always relative to the true/accepted value, not your own measurement.
Keeping a negative sign - percent error uses absolute value, since it measures the size of the gap, not its direction.
Frequently asked questions
What counts as a "good" percent error?
It depends entirely on the context - some scientific measurements aim for well under 1% error, while other estimates might reasonably accept 10% or more. There's no universal threshold.
What's the difference between percent error and percent difference?
Percent error compares a measurement to a known true value. Percent difference compares two measured values where neither is considered the "correct" one, and typically divides by the average of the two instead.
Can percent error be zero?
Yes - a percent error of 0% means your measured value exactly matched the accepted value.
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