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Percent Error Calculator | Compute Absolute And Relative Error

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Calculate percent error between a measured and accepted value with the absolute-value formula shown, plus the absolute difference. The standard lab-quality metric for calibration and experiment accuracy.

Last updated: July 2026 · Free · No sign-up required

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Results

Enter values above and click Calculate to see your result instantly.

Quick reference

MeasuredActualPercent error
9.5105%
1051005%
3.03.141594.51%
9.819.80.10%

info Percent Error Calculator

Free math calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

Percent errorTypical reading
Under 1%Excellent agreement — precision instrument territory
1–5%Good for classroom labs and field measurements
5–10%Acceptable for rough estimates; check method
Over 10%Large — look for systematic error in the setup

lightbulb Worked example

Let's say you are using the Percent Error Calculator. Computes the percentage error between a measured value and an actual value. Enter both values, and the tool applies the formula |measured − actual| ÷ actual × 100 to return the absolute and relative Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Percent error = |measured − actual| ÷ |actual| × 100 and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Percent error = |measured − actual| ÷ |actual| × 100

The Percent Error Calculator is built on a well-established calculation method. It uses the formula Percent error = |measured − actual| ÷ |actual| × 100 to turn your inputs into a reliable result. Computes the percentage error between a measured value and an actual value. Enter both values, and the tool applies the formula |measured − actual| ÷ actual × 100 to return the absolute and relative error, with the sign The steps are shown on the page so you can follow the reasoning from input to output.

  1. Enter the measured (observed/experimental) value.
  2. Enter the actual (true/accepted) value.
  3. The calculator takes the absolute difference, divides by the actual value, and multiplies by 100.

Worked example: measured 9.5, actual 10 → |9.5 − 10| = 0.5; 0.5 ÷ 10 = 0.05; × 100 = 5% error (signed −5%, an undershoot).

Authoritative source: Wolfram MathWorld

Frequently asked questions

What is the percent error formula?
The Percent Error Calculator uses the standard Percent error = |measured − actual| ÷ |actual| × 100. You enter your values, and the calculator applies the formula step by step, showing the working so you can verify the math and understand how the result is derived rather than trusting a black box.
Can percent error be negative?
The Percent Error Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Computes the percentage error between a measured value and an actual value. Enter both values, and the tool applies the formula |measured − actual| ÷ actual × 100 to return the absolute and relative error, with the sign convention and the working shown for There is no limit on usage, and it works on any device.
What is the difference between percent error and percent difference?
Percent error compares a measured value against an accepted reference: |measured − actual| ÷ |actual| × 100, with a clear 'correct' target. Percent difference compares two measured values symmetrically: |a − b| ÷ ((a + b) ÷ 2) × 100, with no reference value, dividing by the average. Use percent error for lab measurements against a standard, and percent difference for comparing two methods or estimates.
What is a good percent error?
It depends on the field and the instrument: physics labs often accept 5–10%, analytical chemistry aims under 1–2%, and engineering measurements target well under 1%. A small percent error means your measurement is close to the accepted value. Errors above 20% usually signal a procedural issue — wrong units, calibration, or technique — rather than random variation.
What happens if the actual value is zero?
Yes — the Percent Error Calculator is fully responsive and works in any modern browser on a phone, tablet, or desktop, with touch-sized inputs and no app to install. The full calculation runs on the device, so you get the same speed and precision on mobile as on a computer, even with a weak connection.
How do I calculate percent accuracy from percent error?
Accuracy = 100% − |percent error|. Measuring 9.6 V on a true 10 V source is a 4% error, i.e. 96% accuracy. Keep the absolute value — direction of the miss doesn't change accuracy — and remember the denominator is the true value, not your measurement; using the wrong base flatters bad measurements.
Can percent error ever be negative?
No — the absolute value in the numerator forces the result to be zero or positive. The sign would tell you the direction (measured above vs. below the true value), but percent error deliberately discards direction and reports only the size of the miss.
What is the difference between percent error and percent deviation?
The arithmetic is identical; the words describe the context. 'Error' is used when comparing against a true or accepted value (a lab standard), while 'deviation' usually compares against a reference, average, or expected figure in quality checks.
What counts as a good percent error in a lab report?
It depends on the instruments. Under 5% is generally respectable in school labs, under 1% is expected with good analytical equipment, and some fields accept 10% or more for rough field measurements. Compare your result against your instrument's stated precision, not an arbitrary bar.
Why divide by the actual value instead of the measured one?
Because the accepted value is the baseline reality — you are asking 'how far off was I relative to what the quantity truly is?' Dividing by the measured value instead would make the same physical miss look smaller or larger depending on which way you erred.

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