Free Calculators Hub
Percent Error Calculator
Percent error is absolute experimental-minus-theoretical difference divided by the absolute theoretical value, times 100. Also reports signed relative error.
Limitation: Educational lab arithmetic.
How to Calculate Percent Error
Enter the measured experimental value and the accepted theoretical value. The primary result is absolute percent error; details show signed relative error and the raw absolute difference.
Enter the experimental (measured) value.
Theoretical cannot be zero
Division by a zero accepted value is undefined. Choose a different reference or report absolute error only outside this tool.
Absolute vs Signed Error
Percent error is always non-negative. Signed relative error keeps the sign of (experimental − theoretical), so underestimates are negative.
Worked Percent Error Examples
Slight underestimate
Inputs
% error
|9.8 − 10| / 10 × 100 = 2%; signed relative error −2%.
Overestimate
Inputs
% error
|12 − 10| / 10 × 100 = 20%.
Exact match
Inputs
% error
Absolute and signed errors are zero.
Related tools
For percent-of questions use Percentage Calculator; for applying a change use Percentage Change.
Frequently Asked Questions
Still have questions about this calculation?
Try the CalculatorPercent Error Formula
Standard introductory lab definition using the absolute theoretical magnitude in the denominator.
Formula
Percent error
% error = |E − T| ÷ |T| × 100
Signed relative error
signed % = (E − T) ÷ |T| × 100
Scientific Background
Some courses omit absolute values or use a different reference (for example average of E and T). This worksheet follows the common |E−T|/|T| form.
Sources & review
Percent Error Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.
Last reviewed
July 22, 2026
Free Calculator Hub methodology
Free Calculator Hub
/methodology
See our methodology and corrections policy.