Instantly find how far your measurement is from the true value
Values
The value you measured or observed
The known or accepted true value (must not be zero)
Result
Your measurement is lower than expected
Formula
Percent Error = |Experimental − Theoretical| / |Theoretical| × 100
The percent error calculator finds how far an experimental (measured) value deviates from a theoretical (accepted) value, expressed as a percentage. Used widely in science, engineering, and quality control, percent error instantly reveals the accuracy of a measurement. Enter your two values and get the result — unsigned for labs, or signed to show whether you over- or under-estimated.
Percent Error = |Experimental − Theoretical| / |Theoretical| × 100. The absolute value signs make the result positive (unsigned), which is the standard convention in most scientific reports.
It depends on the context. In most chemistry or physics labs, under 5% is considered good accuracy. Under 1% is excellent. Above 10% usually indicates a significant systematic error or incorrect procedure.
The unsigned form is always positive or zero. If you enable the signed option, a negative percent error means your measurement was lower than the accepted value (underestimate), while positive means it was higher (overestimate).
Percent error divides by the theoretical value, so if that value is zero the result is mathematically undefined (division by zero). In such cases, use absolute error alone to describe the deviation.