Percent Error Calculator
Lab classic: how far is your measurement from the accepted number? Click any i for detail.
Values
Experimental value
i
Experimental
What you measured or calculated in the lab. |
|
|---|---|
True / accepted value
i
True
Reference or theoretical value. Must be non-zero. |
How to use this calculator
- Enter the experimental result.
- Enter the true or accepted value.
- Read absolute percent error.
- Compare against your lab’s tolerance band.
Results explained
Percent error measures relative disagreement: absolute difference divided by the absolute true value, times 100. It ignores direction (high vs low). Some courses also ask for percent difference between two experimental means — that is a different formula.
Quick reference: percent error
|experimental − true| / |true| × 100.
| Item | Detail |
|---|---|
| Same sign error | Still uses absolute values |
| True = 0 | Undefined — cannot divide by zero |
| 2% vs 20% | Context depends on the instrument |
| Signed error | Use (exp − true)/true if your rubric wants direction |
Follow your lab manual if it defines a signed or relative percent difference instead.
How the estimate is built
% error = |experimental − true| / |true| × 100.
Example scenario
Experimental 9.6, true 9.8 → |9.6−9.8|/9.8 × 100 ≈ 2.04%.
FAQ
Is percent error the same as percent difference?
No. Percent difference usually compares two experimental values using their average in the denominator.
Should I keep the sign?
Absolute percent error is unsigned. Some instructors want a signed relative error — check the rubric.
What if my true value is negative?
The formula uses absolute values, so a negative accepted number still works.
How many decimals should I report?
Match significant figures or the precision your instructor specified.