Percent Error Calculator

1. Enter the measured value, what you observed.
2. Enter the true value, the accepted or correct figure.
3. Read the percent error, how far off the measurement is.
4. See the absolute error and whether it is an over or underestimate.

Here is what each result means:

Percent error measures how far a measured value is from the true or accepted value, expressed as a percentage. It scales the raw error by the size of the true value, so a small error on a large quantity reads as a small percentage. Measuring 9.8 for a value that is really 9.81 gives a percent error of about 0.1 percent.

It is a standard way to report accuracy in science and engineering. Because it uses the absolute value, percent error is never negative; a separate note on direction tells you whether the measurement was too high or too low. A low percent error means the measurement is close to the truth.

It divides the size of the error by the true value and turns it into a percentage.

1. Subtract the true value from the measured value.
2. Take the absolute value and divide by the true value.
3. Multiply by 100 for a percentage.

For a plain change between two numbers rather than a measurement error, the percentage increase calculator is the right tool.

You measure gravity as 9.8, and the accepted value is 9.81.

Calculation: the absolute error is |9.8 - 9.81| = 0.01. Dividing by 9.81 and multiplying by 100 gives 0.01 / 9.81 x 100 = 0.10 percent. The measurement is a slight underestimate but very accurate.

Percent error gives a quick read on accuracy, though the right target depends on the field.

These bands are a rough guide. A physics lab may want under 1 percent, while a rough field estimate may accept far more.

They look similar but answer different questions.

Use percent error when there is a correct value to compare against, and percentage change when tracking growth or decline over time.

The Size of the True Value

The same absolute error is a smaller percentage against a larger true value.

The Measurement Gap

A bigger difference between measured and true raises the percent error directly.

Which Value Is the Reference

Percent error divides by the true value, not the measured one, so the reference matters.

Science Labs

Report how close a measured result is to the accepted value.

Engineering and Quality

Check a reading against a specification or standard.

Estimation

See how far an estimate landed from the real figure.

1. Dividing by the Measured Value

Percent error divides by the true value, not the one you measured.

2. Forgetting the Absolute Value

Percent error is never negative. Take the absolute value of the difference.

3. Confusing It with Percentage Change

Percent error needs a known true value; percentage change compares an old and new figure.

4. Using a True Value of Zero

The formula divides by the true value, so it cannot be zero.

5. Ignoring Direction

Percent error hides whether you were high or low. Note the direction separately if it matters.

The arithmetic is exact; only the displayed decimals are rounded.

It measures how far a measured value is from the true value, as a percentage of the true value. It uses the absolute difference, so it is never negative. Measuring 9.8 against 9.81 gives about 0.1 percent.

Subtract the true value from the measured one, take the absolute value, divide by the true value, and multiply by 100. This tool does it and also shows the absolute error.

Yes. The formula uses the absolute value of the difference, so percent error is never negative. A separate note tells you whether the measurement was too high or too low.

By the true, accepted value, not the measured one. Percent error asks how far the measurement is from the known correct figure.

It depends on the field. Under 1 percent is very accurate, 1 to 5 percent is fine for most work, and above 10 percent is large. A physics lab often aims for under 1 percent.

Percent error compares a measurement to a known true value and is always positive. Percentage change compares an old value to a new one and can be positive or negative.

Because the formula divides by the true value, and dividing by zero is undefined. If the accepted value is zero, percent error cannot be computed.

It is the raw gap between the measured and true values, without dividing by anything. Percent error scales this absolute error by the true value to give a percentage.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Approximation error (Wikipedia).
• Percentage error explained (Maths Is Fun).
• Measurement uncertainty (Wikipedia).