Percent error calculator with signed difference
Enter an observed result and the accepted reference. HitEquals shows absolute percent error, signed error, raw difference and whether the observation is above or below the reference.
Inputs used by this calculator
Percent Error Calculator uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Observed or experimental value | 9.5 | Any finite number supported by the formula | Supplies the observed or experimental value quantity used by the published equation or result breakdown. |
| Accepted or reference value | 10 | Any finite number supported by the formula | Supplies the accepted or reference value quantity used by the published equation or result breakdown. |
How to calculate percent error
Subtract the accepted value from the observation, divide by the magnitude of the accepted value and multiply by 100. Absolute percent error discards direction; signed error preserves it.
Percent error formula
Use the accepted magnitude in the denominator so a negative reference does not reverse the meaning of the percentage scale.
signed error % = (observed−accepted)/|accepted| × 100absolute error % = |observed−accepted|/|accepted| × 100Positive and negative error
A positive signed result means the observation is above the accepted value. A negative result means it is below. The absolute result is useful when only magnitude matters.
Zero accepted value
Division by zero is undefined. When the reference is zero, report the absolute difference or use an error measure designed for that context.
Accuracy and precision
A small percent error indicates closeness to the chosen reference. It does not by itself measure repeatability, uncertainty or whether the reference is correct.
What the Percent Error Calculator answers
Compare an observed value with an accepted value using signed and absolute percent error.
Use Percent Error Calculator when you know Observed or experimental value and Accepted or reference value and need the relationship expressed by the published equation.
Error measures
| Measure | Keeps direction | Reference |
|---|---|---|
| Signed percent error | Yes | Accepted magnitude |
| Absolute percent error | No | Accepted magnitude |
| Absolute difference | Yes as sign | No denominator |
Frequently asked questions
What is percent error?
It is the difference from an accepted value expressed as a percentage of that reference magnitude.
Can percent error be negative?
Signed percent error can; absolute percent error cannot.
Why use the absolute accepted value?
It keeps the denominator positive while direction remains in the numerator.
What if the accepted value is zero?
Percent error is undefined because division by zero is impossible.
Is percent error the same as percent difference?
No. Percent difference treats both values symmetrically and uses their average magnitude.
What question does this Percent Error Calculator answer?
Compare an observed value with an accepted value using signed and absolute percent error.
What to keep in mind
Percent error is undefined when the accepted value is zero. Preserve meaningful measurement precision when reporting.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.