Enter your experimental and theoretical values to calculate the percent error.
How to Use the Percent Error Calculator
Experimental and theoretical values are the two fields — order matters, since percent error is measured against the theoretical number, not averaged between the two.
percent error = |experimental − theoretical| ÷ |theoretical| × 100Measure 24 when the accepted value is 25, and the gap is |24−25| ÷ 25 × 100 — 4%. This Percent Error Calculator runs that comparison for any experimental-versus-theoretical pair. The absolute value strips out direction on purpose: overshooting and undershooting by the same margin should read as the same error, not a plus or a minus.
Why divide by the theoretical value and not the measured one? Because the theoretical value is the fixed target everything's being judged against — dividing by the experimental number instead would make the percentage wobble depending on how far off the measurement already was, which defeats the point.
There's no universal "good" threshold here, whatever a textbook might imply. A school chemistry lab might treat under 5% as fine; precision engineering wants far less. Percent error is a diagnostic, not a pass/fail line.