Soundex & Metaphone
Phonetic hash a word with Soundex and Metaphone.
Overview
Compute the Soundex and Metaphone phonetic codes for any word. Both algorithms hash a word to a short code that represents roughly how it sounds, so misspelled or similar-sounding names end up with the same code. "Robert" and "Rupert" both Soundex to R163; "Smith" and "Smyth" both Metaphone to SM0.
Genealogists searching old records where surnames are spelled inconsistently, data engineers building fuzzy-match indexes on names, and developers writing autocomplete or spell-check engines all use phonetic hashing. It's how many large customer databases handle "did you mean?" suggestions.
How it works
Soundex was patented in 1918 for the US Census and is the original phonetic algorithm. The rules: keep the first letter; map B/F/P/V to 1, C/G/J/K/Q/S/X/Z to 2, D/T to 3, L to 4, M/N to 5, R to 6; drop vowels and H/W; collapse adjacent duplicates; truncate or pad to four characters.
Metaphone (1990) improves on Soundex with better handling of English-specific patterns — silent letters, "PH" → F, "GH" — at the cost of more complex rules. Double Metaphone adds support for many non-English names by emitting two codes per word.
Worked example: Soundex for "Robert" — R, then O/E dropped, B → 1, R → 6, T → 3. Drops, then result is "R163".
Examples
Word: Robert
Soundex: R163
Metaphone: RPRT
Word: Smith / Smyth
Soundex: S530 (both)
Metaphone: SM0 (both)
Word: Knight
Soundex: K523
Metaphone: NT (silent K and GH handled)
FAQ
Should I use Soundex or Metaphone?
Metaphone is usually better — Soundex has known weaknesses with vowel-heavy names and inconsistent handling of clusters. Soundex is more widely supported in legacy databases (SQL Server, Oracle ship it built-in).
Are there algorithms tuned for non-English names?
Yes. Double Metaphone handles Slavic, Germanic, Romance, and some other patterns. NYSIIS is another option. Beyond that, you may need language-specific phonetic systems.
Why do my results differ from another tool?
The original Soundex has several variants — American Soundex, Daitch-Mokotoff, Refined Soundex. Make sure both tools are running the same flavour.