Percent Error Calculator

Percent error and percent difference, which are not the same.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Your measured value

Accepted or true value

The reference figure you are checking against. Cannot be zero — there is nothing to take a percentage of.

Percent error

5.000%

Your measurement read low

Percent error5.0000%

Absolute error0.5

Signed error-0.5

Percent difference5.1282%

DirectionUnder

Percent error and percent difference are not the same calculation and get confused constantly. Percent error compares a measurement to a value you trust, and divides by that trusted value. Percent difference compares two measurements where neither is authoritative, and divides by their mean. Use percent error for a lab result against a literature value; use percent difference when comparing two runs of the same experiment. Percent error is conventionally reported unsigned, but the direction is worth knowing — a consistent bias in one direction points at a calibration problem rather than random scatter.

How the Percent Error Calculator works

Enter your measured value and the accepted one to get percent error, the absolute error and the direction of the bias. It also shows percent difference, because the two are constantly confused and they divide by different things.

Also known as: percentage error calculator · experimental error calculator · percent difference calculator · how to calculate percent error

Where to go next

The Percent Error question rarely arrives on its own. These are the ones that usually come with it:

Relative Standard Deviation Calculator — RSD and coefficient of variation for replicate measurements.
Speed Distance Time Calculator — Any one of the three from the other two, in four units.
Acceleration Calculator — Acceleration in m/s² and in g, which is the legible one.
Free Fall Calculator — Fall speed and time, with the air resistance caveat stated.

Sources

Frequently asked questions

How do I calculate percent error?

Take the difference between your measurement and the accepted value, divide by the accepted value, and multiply by 100. Measuring 9.5 where the true value is 10 gives 5% error.

What is the difference between percent error and percent difference?

Percent error divides by a value you trust. Percent difference divides by the mean of two values where neither is authoritative. Use error for a result against a literature value, difference for two runs of the same experiment.

Should percent error be negative?

It is conventionally reported unsigned, since it measures how far off you were rather than which way. The direction still matters though — a bias consistently one way points at a calibration problem rather than random scatter.

What counts as a good percent error?

It depends entirely on the method. Analytical balance work should be well under 1%, a titration under 2%, and a rough volumetric estimate might reasonably be 5%. There is no universal threshold.

Put this calculator on your own site

Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.

The one-line version

<iframe src="https://www.thecalclibrary.com/embed/percent-error-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Percent Error Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;margin:6px 0 0;color:#64748b">Powered by <a href="https://www.thecalclibrary.com/percent-error-calculator" style="color:#64748b">Percent Error Calculator</a> from The Calc Library</p>

The only condition is that the credit line below the frame stays in place. That one line is what pays for the tool being free — it is how anyone else finds it.