What you recorded.
The known or accepted value.
Formula and worked example
Percent Error = |Observed − Actual| / |Actual| × 100
Example: A student weighs a sample and gets 23.5 g. The accepted (actual) mass is 25 g.
Step 1 — Find the difference: 23.5 − 25 = −1.5
Step 2 — Take the absolute value: |−1.5| = 1.5
Step 3 — Divide by the actual value: 1.5 ÷ 25 = 0.06
Step 4 — Convert to a percentage: 0.06 × 100 = 6% error
Frequently asked questions
How do you calculate percent error?
Subtract the actual value from the observed value, take the absolute value of that result, divide it by the absolute value of the actual value, then multiply by 100. In short: |Observed − Actual| ÷ |Actual| × 100.
What is a percentage error?
Percentage error measures how far a measured or estimated value sits from the true or accepted value, expressed as a percentage. It converts a raw difference into a relative figure, which makes it easier to judge accuracy regardless of the units or scale involved.
How to calculate 95% error?
Percent error itself has no separate "95% error" formula — a result of 95% just means the standard calculation above produced 95%. If you actually mean the 95% confidence interval used in statistics, that's a different calculation: margin of error = 1.96 × (standard deviation ÷ √sample size). Check which one your assignment is asking for before you calculate.
What counts as a good percent error?
It depends on context. School lab work typically treats under 5% as acceptable, precision engineering and calibrated instruments often expect under 1%, and field or exploratory measurements may tolerate 10% or more. Use the tolerance your instructor or standard specifies rather than one fixed number.
Can percent error be negative?
Not with the standard formula, since the absolute value keeps the result at zero or higher. If you skip the absolute value and calculate (Observed − Actual) ÷ Actual × 100 instead, a negative sign shows your observed value was lower than the actual value, and a positive sign shows it was higher.