Soundex

Soundex is a phonetic algorithm used to index names by their pronunciation rather than their spelling. It was developed in the early 20th century to help match names across spelling variations in large datasets, such as census records and library catalogs. The most common variant is known as American Soundex, and it remains a reference point in many genealogy and data-minding applications.

The standard Soundex encoding produces a four-character code: the first letter of the name followed by three digits. To generate it, the first letter is kept as the initial code. Each subsequent letter is mapped to a digit according to a fixed set of rules (for example, B, F, P, V map to 1; C, G, J, K, Q, S, X, Z map to 2; D and T map to 3; L to 4; M and N to 5; R to 6). Vowels and the letters H, W, and Y are not coded. After mapping, noncoding letters are ignored, consecutive identical digits are collapsed to a single digit, and any zeros are removed. The result is truncated or padded with zeros to fit three digits after the initial letter.

Variants and usage: American Soundex is the most widely cited standard, but several variations exist, including Refined Soundex, which tweaks the encoding rules to reduce collisions and improve accuracy for certain name groups. Soundex remains in use for historical data analysis, matching surnames across spellings, and supporting search systems where exact spelling varies.

Limitations: Soundex can produce false positives for names that sound similar but are unrelated, and it can fail for non-English names or names with complex pronunciations. Despite limitations, Soundex provides a simple, language-agnostic first-pass tool for phonetic matching. Example codes include Robert -> R163, Ashcraft -> A261, Pfister -> P236.