Soundex Calculator, Phonetic Name Coding

Soundex is a phonetic algorithm that indexes names by sound rather than spelling, so that homophones, names that sound alike but are spelled differently, receive the same code. It was patented by Robert C. Russell in 1918 and later adopted by the U.S. National Archives to index the Federal Census; today the same rules power the SOUNDEX() function in SQL databases. Every code is exactly four characters: one letter followed by three digits.

The tool applies the National Archives rules in order:

1. Retain the first letterof the name as the code's leading character.
2. Map the remaining letters to digits using the fixed table:
   • 1 → B, F, P, V
   • 2 → C, G, J, K, Q, S, X, Z
   • 3 → D, T
   • 4 → L
   • 5 → M, N
   • 6 → R
   • not coded → A, E, I, O, U, Y, H, W
3. Collapse adjacent equal codes.Two or more letters in a row that map to the same digit are coded only once. This also applies to the first letter: if the second letter shares the first letter's code, it is not coded again (this is why the f in Pfister is dropped).
4. H and W are transparent. Two letters with the same code separated only by an H or W are treated as adjacent and coded once, the rule that collapses the s and c in Ashcraft into a single 2.
5. Vowels separate. Two letters with the same code separated by a vowel (A, E, I, O, U or Y) are coded twice, because the vowel breaks the run, the reason both n and m survive in Honeyman.
6. Fix the length to four. If fewer than three digits were produced, pad with trailing zeros; if more than three, keep only the first three.

To keep the result trustworthy, the calculator computes each code with two independent implementations, a single-pass state machine that also produces the derivation table, and a separate marker-and-collapse method, and only displays a code when both agree. The letter-by-letter derivation shown on-screen is the actual decision log from the coder, not a re-explanation.

• U.S. National Archives (NARA): The Soundex Indexing System
• U.S. Census Bureau: Soundex coding description

The letter-to-digit table and the H/W and vowel separator rules were last cross-checked against the NARA and Census sources on 2026-07-16. Soundex is a fixed historical standard, so these rules do not change; the calculator's worked examples (Smith/Smyth → S530, Robert/Rupert → R163, Ashcraft/Ashcroft → A261) match the codes published in those sources.