Word Error Rate Calculator

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

About Word Error Rate Calculator

Word error rate is the Levenshtein distance between the recognised and reference word sequences, normalised by the reference length. Because insertions are counted but do not lengthen the denominator, WER can exceed 100 percent when a system hallucinates extra words. Aligning the hypothesis to the reference first is what produces the substitution, deletion and insertion counts.

Formula

Word error rate

WER = (S + D + I) / N

S: Substituted words
D: Deleted words
I: Inserted words
N: Words in the reference

Worked example

With the default values below, Word Error Rate Calculator returns Word error rate of 10.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Substitutionsminimum 0: 12
Deletionsminimum 0: 5
Insertionsminimum 0: 3
Words in the reference transcriptminimum 1: 200

Results

Word error rate: 10.00%
Total word errors: 20
Word accuracy: 90.00%
Errors per 100 reference words: 10.00

Step by step

1Values used
2Word error rate
3Word error rate= 10.00
4Total word errors= 20
5Word accuracy= 90.00
6Errors per 100 reference words= 10.00

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 2 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

Can WER be above 100 percent?

Yes. A system that inserts many spurious words can accumulate more errors than there are reference words, which is why accuracy is reported as 1 - WER and may go negative.

How should I normalise text first?

Apply consistent casing, expand or remove punctuation, and standardise numbers and contractions. Comparing WER figures produced under different normalisation rules is meaningless.