Compare an experimental value to a true or theoretical value and get the percent error and absolute error instantly, computed in your browser.
Percent Error Calculator Online
Compare an experimental value to a true or theoretical value and get the percent error and absolute error instantly, computed in your browser.
The Percent Error Calculator runs entirely in your browser. The experimental and theoretical values you enter are never uploaded or sent to ArrayKit — everything is computed on your device.
The Percent Error Calculator compares a measured (experimental) value against a true or theoretical value and reports how far off the measurement is, both as a percentage and as an absolute difference. Type in the two numbers and the tool applies the standard percent error formula — absolute error divided by the theoretical value, times 100 — so you can see at a glance how accurate a lab measurement, estimate, or calculation actually is. It flags the special case where the theoretical value is zero, since percent error is undefined by division, and still shows the absolute error so the comparison is not lost. Handy for chemistry and physics lab reports, engineering tolerance checks, and any situation where you need to quantify measurement accuracy against an accepted value. Everything runs locally in your browser — your numbers stay on your device.
Features
Enter an experimental value and a theoretical (true) value
Instantly computes percent error using the standard formula
Also shows the absolute error between the two values
Handles negative experimental and theoretical values correctly
Warns when the theoretical value is zero, since percent error is undefined
Copy a plain-text summary of both results with one click
Clear error messages for missing or non-numeric input
Runs entirely in your browser with no data sent anywhere
How to use the Percent Error Calculator
Enter the experimental (measured) value in the first field
Enter the theoretical (true or accepted) value in the second field
Read the percent error and absolute error in the results panel
Copy the summary to paste into a lab report or spreadsheet
Example
Input
exp 9.8, true 9.81
Output
Percent error: 0.10%
Common errors & troubleshooting
The result shows 'Undefined' for percent error. — This happens when the theoretical value is 0 — percent error divides by the theoretical value, so it cannot be computed. The absolute error is still shown.
The percent error looks unexpectedly large. — Double-check which value is experimental and which is theoretical — the Percent Error Calculator always divides by the theoretical (true) value, not the measured one.
Negative values give a confusing percent error. — The calculator uses the absolute difference and the absolute theoretical value, so a negative sign on either input does not flip the sign of the result — only the magnitudes matter.
Frequently asked questions
What formula does the Percent Error Calculator use?
Percent error = |experimental − theoretical| ÷ |theoretical| × 100. The calculator also shows the absolute error, which is just |experimental − theoretical| without the percentage step.
What counts as a 'good' percent error?
It depends on the field and instrument — in many school chemistry or physics labs, under 5% is considered acceptable, but tighter engineering tolerances may require well under 1%. The Percent Error Calculator only computes the number; interpreting it is context-specific.
Why does the Percent Error Calculator show 'Undefined' sometimes?
Percent error divides by the theoretical value. When that value is 0, the division is undefined, so the calculator flags it and shows only the absolute error instead of a percentage.
Is percent error the same as relative error?
They are closely related: relative error is the absolute error divided by the theoretical value as a decimal, and percent error is that same ratio expressed as a percentage. The Percent Error Calculator reports the percentage form.
Can the Percent Error Calculator handle negative measurements?
Yes. Both the experimental and theoretical fields accept negative numbers, and the calculator uses absolute values in the formula so the result is always a non-negative percent error.
Does the Percent Error Calculator send my measurements anywhere?
No. All calculations happen locally in your browser. The values you type into the Percent Error Calculator are never uploaded to ArrayKit or any server.
Related tools
Percentage Calculator — Solve percentage problems: X% of Y, X is what % of Y, and percent change.
Standard Deviation Calculator — Calculate population and sample standard deviation, variance and mean of a data set.
Rounding Calculator — Round numbers to decimals, significant figures or the nearest multiple.