SOUNDEX CODES

The soundex is a four character code based on the way a name sounds rather than 
the way it is spelled. Surnames that sound the same but are spelled different-
ly, like SMITH and SMYTH, have the same code and are indexed together. The 
Soundex Coding system was developed so that you can find a surname no matter 
how it was spelled. [Soundex coding is used for most of the microfilmed indexes 
of U.S. census records.]

Every Soundex code consists of a letter and three numbers, like B560. The
letter is always the first letter of the surname. The numbers are assigned
this way:
         
          1  =  b,p,f,v      2  =  c,s,k,g,j,q,x,z
          3  =  d,t          4  =  l
          5  =  m,n          6  =  r
          disregard  -  a,e,i,o,u,w,y,h

To figure out your surname's code, do this:        (JOHNSON)
   - Eliminate any a,e,i,o,u,w,y,h                 (JNSN)
   - Write the first letter, as is, followed
     by the codes found in the table above         (JNSN = J525)

No matter how long or short the surname is, the soundex code is always the 
first letter of the name followed by three numbers. If you have coded the first 
letter and three numbers but still have more letters in the name, ignore them. 
If you have run out of letters in the name before you have three numbers, then 
add zeroes to the code. 

            WASHINGTON = WSNGTN = W252 (ignore the ending TN)
            KUHNE = KN = K500 (add zeroes to the end)

Prefixes: You have a surname with a prefix like Van, Von, De, Di, or Le. Code 
it with and without the prefix because it may be listed under either code. Van 
Hoesen should be coded as VanHoesen and also as Hoesen. Mac and Mc are NOT 
considered prefixes. 

Double letters: Any double letters side by side should be treated as one 
letter. For example Lloyd is coded as if it was spelled Loyd. Gutierrez is 
coded as if it was Gutierez. 

Side by side letters with the same value: You may have different letters side 
by side that have the same code value. For example PFISTER (P & F are both 1), 
JACKSON (CKS are all 2). These letters should be treated as one letter.  
PFISTER is coded as PSTR and JACKSON is coded as JCN. 

From "Beginnning Your Genealogical Research in the National Archives," courtesy 
ROOTS-BBS, CA, Brian Mavrogeorge, sysop.