Percent Error Calculator – Accurate & Free Calculation

Have you ever measured something in a lab experiment, only to find your result didn’t quite match the “true” or “accepted” value? That’s where percent error comes in. It tells you how far off your measured value is compared to the actual value, expressed as a percentage. With the Percent Error Calculator, you can quickly check your accuracy, whether you’re in a science class, a chemistry lab, or working with real-world data.

Why Percent Error Matters

Percent error is one of the most common ways to evaluate accuracy and reliability in measurements. It is used in:

• Education & Exams: Physics, chemistry, and biology labs often require calculating error.
  
• Research & Experiments: Scientists use it to compare experimental results to theoretical values.
  
• Engineering & Manufacturing: Ensures precision when building or testing products.
  
• Everyday Life: From checking a scale’s accuracy to comparing fuel efficiency, percent error shows how close results are to reality.
  

By knowing your percent error, you can identify mistakes, refine methods, or confirm that your results are within acceptable limits.

What You Enter in the Calculator

The calculator is simple — it needs just two values:

• Experimental (Measured) Value: The value you observed or calculated in your test.
  
• True (Accepted) Value: The correct, known, or standard value.
  

Once you enter these, the calculator instantly computes the percent error.

Example

• Chemistry: You titrated a solution and found 24.8 mL instead of the expected 25.0 mL → error = 0.8%.
  
• Physics: You measured acceleration due to gravity as 9.6 m/s² instead of 9.8 m/s² → error = 2.04%.
  
• Everyday life: Your bathroom scale says 155 lbs, but at the doctor’s office, it’s 150 lbs → error = 3.33%.
  

FAQs – Questions About Percent Error

1. What is a good percent error?
Usually less than 5% is considered very good. Anything under 10% is often acceptable in experiments.

2. Can percent error be negative?
No. Because of the absolute value, percent error is always positive.

3. What if my error is over 100%?
It means your measurement was more than double the true value — likely a major mistake or wrong unit.

4. Why do we use absolute value?
To focus on the size of the error, not whether it’s above or below the true value.

5. How is percent error different from percent difference?
Percent error compares your value to a true/known value. Percent difference compares two experimental values.

6. Do I need percent error in school labs?
Yes — it’s a standard requirement in physics, chemistry, and biology reports.

7. What if I don’t know the true value?
You can’t calculate percent error without a known correct value. In that case, use percent difference instead.

8. Can I use this for business or finance?
Yes — percent error can measure forecast accuracy (e.g., predicted vs. actual sales).

9. Does rounding affect percent error?
Yes. Always keep enough decimal places when entering values for the most accurate result.

10. Can this calculator handle negative inputs?
Yes — the formula uses absolute values, so negative numbers are converted automatically.