NEW YORK – The top U.S.-based retailers with the highest sales per square foot, a defining metric of brick-and-mortar store productivity, are Apple, Murphy USA and Tiffany & Co., according to data from eMarketer RETAIL, a new information platform the research firm launched last week. The research covers store productivity, sales performance by channel, real estate, digital presence and other indicators for more than 225 U.S.-based retailers.

Apple leads the marketplace by a wide margin, averaging $4,551 in sales per square foot of retail space over the most recent trailing-12-month period, according to data compiled by eMarketer RETAIL.

Number 2-ranked Murphy USA, a national gas and convenience store chain, points up the success of the service station-attached convenience stores, which are physically small and rely largely on tobacco sales for higher revenues. Luxury retailer Tiffany & Co. then comes in a distant third, with the remainder of the top 15 all banking less than $2,000 in sales per square foot over the past year. Slots four through 15 include a variety of retail sectors, from apparel and accessories and luxury goods, to jewelry and luggage.

Most of the companies that grace the top 15 in sales per square foot are well-established retailers, evidenced by the fact that only four of those retailers are also in the top 15 in terms of year-over-year growth in sales per square foot — Michael Kors Holdings, Kate Spade & Co., Vince and Movado, all luxury retailers.

The retailers that are leading the market in sales per square foot growth over the past year are more diverse, ranging from larger-format stores like RH, Sprouts Farmers Market and The TJX Companies’ HomeGoods, to athletic apparel retailers.

To develop its store productivity rankings, eMarketer analyzed quantitative and qualitative data from public filings, company reports, equity analysts and banks, research firms, government agencies and media outlets, weighting each piece of information based on methodology and soundness.