Percent Error Calculator

What This Calculator Does

When you measure something, your result is rarely exactly the true value. Percent error says how far off you were, as a percentage of the true value - so it makes sense whether you are measuring something tiny or huge.

Being off by 2 sounds small, but it depends on the target: 2 away from 50 is a 4% error, while 2 away from 1,000 is only 0.2%. That is why scientists report the percent error after an experiment, not just the raw gap.

Percent Error Formula

$$\text{percent error} = \frac{|\text{measured} - \text{true}|}{|\text{true}|} \times 100$$

The bars mean absolute value, so the result is never negative.

How to Use It

1. Enter the measured value.
2. Enter the true value.
3. Read the percent error.

Worked Examples

Measured	True	Percent error
48	50	4%
105	100	5%
18	20	10%
9.8	9.81	~0.1%

FAQ

How do you calculate percent error?

Subtract the true value from the measured value, take the absolute value, divide by the true value, and multiply by 100. For 48 vs 50: $\frac{|48 - 50|}{50} \times 100 = 4\%$.

Can percent error be negative?

No. The formula uses absolute value, so percent error is always zero or positive.

What is the difference between percent error and percent difference?

Percent error compares a measurement to a known true value; percent difference compares two measurements when neither is the “true” one.