NPD results were released today, and Splatoon debuted in fifth place in the United States. Nintendo failed to release any sort of statement on the sales of either Splatoon, Puzzle & Dragons, or their hardware. As a result, the numbers were leaked by a well-known source on Neogaf. According to the source, during the two days of the counting period (May 29-May 30), Splatoon sold 136,000 units in North America. Obviously, this does not include digital sales in the country.
If you combine these 136,000 units with the 214,000 units sold in Japan, you get an even 350,000 units sold. If European and digital sales are factored in, Splatoon may well have already hit half a million units by now.
In addition, this leaker stated that the Wii U sold 42,000 units in May, indicating that Splatoon failed to make any sort of large sales traction on the hardware side.