What is the Soundex System?

Soundex is a phonetic index that groups together names that sound alike but are spelled differently. For example Stewart and Stuart. Understanding this system can help researchers find names that are spelled differently or inconsistently which is a common genealogical research problem.

The Soundex indexing system was developed by Robert C. Russell and Margaret K. Odell in the early 1900s. Its purpose was to encode homophones (more than one word that has the same pronunciation) to the same representation so that they can be matched despite minor differences in spelling.

The indexing system assigns letters of the alphabet to specific numbers.

   Number   Alphabet Letter
 1 B, F, P, V
 2 C, G, J, K, Q, S, X, Z
 3 D, T
 4 L
 5  M, N
 6  R

Note: The vowels A, E, I, O and U along with the consonants W, H and Y are not coded.

Try it! RootsWeb offers this tool for providing the Soundex code for a surname you provide along with other surnames that share that same code.

A Soundex code for a surname is a letter followed by three numbers.

Sample: W-452. This is the last name Williamson. The “W” represents the first letter in the last name. Other surnames that share this Soundex code are Willihnganz, Willingham and Woolums.

Other rules apply to Soundex and how to handle certain letters in a surname. The National Archives website explains more.

Soundex System and Genealogy

The most well-known genealogical use of Soundex can be seen in the US Federal census records from 1880 to 1930. It is also used by the federal government for selected ship passenger arrival lists, certain Canadian border crossings, and some naturalization records.

A few county governments have also used a version of Soundex for courthouse records. More recently, Ancestry.com and other websites have featured a Soundex search for their online genealogical databases.

Try it! This link will take you the Vitelli Soundex of the U.S. Census collection.

Sites like Ancestry.com and FamilySeach.org apply Soundex in their search forms. You may not see this directly but it explains when your research returns various spelling suggestions and variations of a surname.

I personally see this often with last names in a family that I research; Sisor, Sizer, Seizer, Sizor. These names are pronounced the same but are spelled differently. Annoying? Yes, Helpful? Sometimes. This is proven when I see a probate record that spells it a specific way then I find a deed for that same person with a similar spelling.


It’s also helpful to know that some of our ancestors may have lacked basic reading and writing skills. From this blog on Paleography, which the study of handwriting, spelling wasn’t consistent and standardized until the mid-1800s. Therefore, words were spelled and recorded how they sounded.

Paleography doesn’t work directly with the Soundex System but it’s helpful to understand that handwriting varies from person to person so when documents are transcribed, words may be misspelled or transcribed incorrectly based on what is seen and interpreted.