Character Error Rate Calculator

Work out character error rate instantly with clear inputs, formula shown and shareable results.

About Character Error Rate Calculator

Character error rate applies the same edit-distance ratio as WER but at character granularity, which makes it the standard metric for OCR, handwriting recognition and languages without clear word boundaries such as Chinese and Japanese. CER is always lower than WER on the same output because a single wrong letter costs one character error instead of a whole word.

Formula

Character error rate

CER = (S + D + I) / N where N is the number of reference characters

Worked example

With the default values below, Character Error Rate Calculator returns Character error rate of 5.000%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Character substitutionsminimum 0: 40
Character deletionsminimum 0: 12
Character insertionsminimum 0: 8
Characters in the referenceminimum 1: 1,200

Results

Character error rate: 5.000%
Total character edits: 60
Character accuracy: 95.000%
Edits per 1,000 characters: 50.00

Step by step

1Values used
2Character error rate
3Character error rate= 5.000
4Total character edits= 60
5Character accuracy= 95.000
6Edits per 1,000 characters= 50.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Do spaces count as characters?

That is a convention you must fix and document. Including whitespace is common for OCR; excluding it makes CER slightly lower and is usual for scripts without spaces.

Why is CER better than WER for OCR?

Scanned text often has single-glyph confusions such as rn for m. WER marks the whole word wrong, hiding the fact that recognition was 90 percent correct at the glyph level.