Sales by volume are systematically undercounted in public and private surveys of ecommerce. The twin results are that the contribution of to the ecommerce marketplace is considerably larger than generally assumed and the overall market is larger by this difference. As the costs of selling things online have fallen with cheaper equipment and communications fees, and with the availability of retail platform services provided by eBay, Amazon.com, Google, and many other firms, Internet retailing has grown to include many businesses and individual occasional particularly in the United States. But how much do these small sellers sell each year? U.S. Government statistics give some insight into the type and sales volume of online but the Government's current methods of data collection and analysis are better suited to tracking larger, traditionally organized businesses, rather than small sellers, whether operating as businesses or as individuals. Traditionally, simply were ignored. In traditional retail markets, the number of businesses with low annual revenues may not be significant because the contribution of such to the overall size of the market is relatively small. However, in Internet retailing, there are millions of that, in the aggregate, make a large contribution to the overall market. Yet these are systematically overlooked in government and private data collection and analysis. In this paper, we estimate the size of Internet retailing in 2004 to have been over 20% above U.S. Government estimates - and the difference is explained by a more accurate accounting of sales by sellers. We do this through a variety of methods and the development of confidence intervals in our data. We hope that the techniques outlined in this paper will give greater insight into the magnitude of Internet retailing, particularly in the long tail of the ecommerce market occupied by volume sellers.