What is Soundex?

The Soundex indexing system replaces a surname with a code consisting of a single letter and three numbers. For instance, under the Soundex system, the name “Smith” would be replaced by the code “S350.” The Soundex indexing system went into effect with the 1880 federal census, and is still used today.

Creating a Soundex code

A Soundex code is created by using the first letter of the surname for the letter portion of the code, then assigning a number to the first three remaining consonants in the name. Vowels (A, E, I, O, U) and the letters H, W, and Y are not coded. If fewer than three consonants remain after vowels are discounted, a zero is used for the final digit(s). Here are some examples of the system:

Soundex Coding Guide
The number Represents the letters
1 B, P, F, V
2 C, S, K, G, J, Q, X, Z
3 D, T
4 L
5 M, N
6 R






Remember, vowels (A, E, I, O, U) and the letters H, W, and Y are not coded.

Additional rules

  1. Names with prefixes:
    If your surname has a prefix like Van, De, Di, or Le, code it with and without the prefix. It could appear in an index or the Soundex Reference Guide with or without the prefix. (Note: Mac and Mc are NOT considered prefixes.)
  2. Names with double letters:
    If your surname has any double letters (e.g. Lloyd, Gutierrez, Flynn), the double letters should be treated as one letter. Thus, in the surname Lloyd, the second L should be slashed out; in Gutierrez, the second R; and so on.
  3. Names with letters side by side that share the same number in the Soundex coding guide (shown below):
    For example, the surnames Pfister and Jackson. The letters P and F share the same number (1), as do C, K, and S (the number 2). These letters should be treated as a single letter. Thus, in the name Pfister, the F should be crossed out; in the name Jackson, the K and S should each be eliminated.

Coding examples

Surname: SMITH
Problem: fewer than 3 consonants
First letter of code: S
Vowels and letters to be eliminated: I, H
Consonants to be coded: M, T
M = 5; T = 3; 3rd consonant substitute = 0
Soundex code: S530

Surname: FLYNN
Problem: Double letters
First letter of code: F
Vowels and letters to be eliminated: Y
Consonants to be coded: L, N
L = 4; N = 5; double letter N treated as single letter. 3rd consonant substitute = 0.
Soundex code: F450

If you will be using the 1880, 1900, or 1920 federal Rhode Island censuses on your visit, you may want to code your surnames before you leave home. The reference staff will be happy to help you when you visit.