Table 5.26 – Sales and Service Counters
Current Guidelines:  
7.2 Sales and Service Counters . . .

(1)  In areas used for transactions where counters have cash registers and are provided for sales or distribution of goods or services to the public, at least one of each type shall have a portion of the counter which is at least 36 in (915 mm) in length with a maximum height of 36 in (915 mm) above the finish floor. . . .

(2)  In areas used for transactions that may not have a cash register but at which goods or services are sold or distributed . . . either:

(i)  a portion of the main counter which is a minimum of 36 in (915 mm) in length shall be provided with a maximum height of 36 in (915 mm); or

(ii)  an auxiliary counter with  maximum height of 36 in (915 mm) in close proximity to the main counter be provided; or

(iii)  equivalent facilitation shall be provided . . .
Final Revised Guidelines:  
904.4 Sales and Service Counters.  Sales and service counters shall comply with 904.4.1 or 904.4.2.  The accessible portion of the counter top shall extend the same depth as the sales or service counter top.
Exception:  In alterations, when the provision of a counter complying with 904.4 would result in a reduction of the number of existing counters at work stations or a reduction of the number of existing mailboxes, the counter shall be permitted to have a portion which is 24 inches (610 mm) long minimum complying with 904.4.1 provided that the required clear floor or ground space is centered on the accessible length of the counter.

904.4.1  Parallel Approach.  A portion of the counter surface that is 36 inches (915 mm) long minimum and 36 inches (915 mm) high maximum above the finish floor shall be provided.  A clear floor or ground space complying with 305 shall be positioned for a parallel approach adjacent to the 36 inch (915 mm) minimum length of the counter. 
Exception:  Where the provided counter surface is less than 36 inches (915 mm) long, the entire counter surface shall be 36 inches (915 mm) high maximum above the finish floor. 

904.4.2  Forward Approach.  A portion of the counter surface that is 30 inches (760 mm) long minimum and 36 inches (915 mm) high maximum shall be provided. Knee and toe space complying with 306 shall be provided under the counter.  A clear floor or ground space complying with 305 shall be positioned for a forward approach to the counter.
Model Codes & Standards
ICC/ANSI A117.1-1998:  Section 904.3 has similar requirements for sales and service counters.