The London store has two floors, with womenswear at street level and menswear in the basement.
A UK spokeswoman said that, while every shop is different, with new graphic treatments and internal colour schemes in each, a footprint of about 2,500 sq ft (230 sq m) is likely to become the norm for all future UK branches.
The stores’ designs are created by New York architectural practice JPDA.
A store also opened on Oxford Street this week and it is understood that the retailer is considering another site in Liverpool, although no contracts have been exchanged to date.
American Apparel, which has its headquarters in Los Angeles, arrived in the UK in September 2004 with its first store on Carnaby Street. It now trades from eight stores in the UK and operates in 10 other countries. In the US, it has more than 150 outlets.