Percent Error Formula
Measure experimental accuracy
Formula
% Error = |Experimental - Theoretical| / Theoretical × 100%
- Experimental value = measured result
- Theoretical value = accepted/true value
- Absolute value = always positive error
- Result = percent deviation from true value
Example
Problem: Theoretical density = 2.70 g/cm³, measured = 2.62 g/cm³
% Error = |2.62 - 2.70| / 2.70 × 100%
= 0.08 / 2.70 × 100%
= 0.0296 × 100% = 2.96%
Answer: 2.96% error
Notes
- Lower percent error = higher accuracy (closer to true value)
- Use absolute value to avoid negative errors
- Different from percent yield (which can be < or > 100%)
- Common in lab reports to assess experimental technique