Percent Error: Formula and Examples

Percent error in one line

Percent error tells you how far a measured value is from the true or accepted value, expressed as a percentage.

The standard formula is:

Percent error = |measured - actual| / actual * 100

How to calculate percent error

1. Subtract the actual value from the measured value.
2. Take the absolute value so the result is positive.
3. Divide by the actual value.
4. Multiply by 100.

Example 1

A scale shows 49 kg, but the true value is 50 kg.

• Difference: |49 - 50| = 1
• Divide by actual: 1 / 50 = 0.02
• Convert to percent: 0.02 * 100 = 2%

The percent error is 2%.

Example 2

A lab result is 84, while the accepted value is 80.

• Difference: |84 - 80| = 4
• Divide by actual: 4 / 80 = 0.05
• Convert to percent: 5%

Why absolute value matters

Percent error usually shows the size of the error, not the direction. That is why the formula uses absolute value bars.

Percent error vs percentage difference

Use percent error when you compare a measured value with a true or accepted value.

Use percentage difference when you compare two values and neither is treated as the true reference.

Common mistakes

• Dividing by the measured value instead of the actual value
• Forgetting the absolute value
• Mixing up percent error and percentage change

FAQ

Can percent error be negative?

In the standard form, no. It is usually reported as a positive percentage because it measures the size of the error.

What if the actual value is zero?

The formula breaks because you cannot divide by zero. In that case, you need a different error measure.

Can I calculate percent error with a calculator?

Yes. You can use calculate-percentage.online to compute the percentage once you know the difference and the actual value.