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Saturday, March 14, 2026

Percent Error Calculator

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Percent Error Calculator

Determine the accuracy of your experimental results

How to use the Percent Error Calculator

Percent error is a mathematical calculation used in science and statistics to determine how close an experimental result is to the accepted or true value. To use this tool, enter the **Accepted (Theoretical) Value**, which is the widely recognized correct value (like the constant of gravity, $9.8$ m/s²). Then, enter your **Experimental (Observed) Value**, which is the result you obtained from your actual experiment. When you click **"Calculate Percentage Error"**, the tool applies the standard formula: $$\text{Percent Error} = \left| \frac{\text{Experimental} - \text{Theoretical}}{\text{Theoretical}} \right| \times 100$$. A lower percentage indicates higher accuracy in your experimental methods, while a higher percentage suggests that there may be errors in measurement or external factors affecting the outcome.

  • Absolute Value Logic: The tool automatically ignores negative signs because error is measured by distance from the truth.
  • Lab Ready: Perfect for Physics, Chemistry, and Biology lab reports.
  • Quality Check: Instantly see if your experiment needs to be repeated due to high variance.
Can percent error be negative? +
In most scientific contexts, percent error is expressed as an absolute value (positive). However, some instructors prefer to see a negative sign if the experimental value was lower than the theoretical value. This tool uses the absolute value for standard accuracy reporting.
What is considered a "Good" percent error? +
Generally, a percent error of less than 5% is considered excellent in school and university labs. Errors up to 10% are often acceptable, but anything higher usually requires an explanation in your lab report.
What is the difference between Error and Percent Error? +
"Error" is the raw difference (e.g., you were off by 2 grams). "Percent Error" puts that difference into perspective (e.g., being off by 2 grams in a 100g sample is 2%, but in a 10g sample, it's 20%).
Where do I find Theoretical Values? +
Theoretical values are typically found in textbooks, scientific databases, or the periodic table (e.g., atomic masses or boiling points).
Why is my experimental value so high? +
High errors can be caused by "Systematic Errors" (faulty equipment), "Random Errors" (unpredictable fluctuations), or "Human Errors" (misreading a scale or parallax error).
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