And most of the traffic comes from the iPad.
Special offers site dealnews says Americans spend around 38 per cent more time shopping on their mobile devices in summer – perhaps a result of buying bargains on-the-move during on sunny days out.
In fact, 22.5 per cent of total dealnews site traffic came from mobile devices on last month's Independence Day (July 4th), the highest across the season for both 2012 and 2011.
That's equivalent to a 43 per cent rise on average weekday mobile traffic, while the iPad accounted for 40 per cent of all visits on the day, ahead of 30 per cent and 26 per cent for the iPhone and Android devices, respectively.
Dan de Grandpre, CEO of dealnews, said: "Since more people are shopping from their mobile devices now than ever before, it's imperative that retailers and merchants invest in dedicated mobile sites to improve consumers' mobile shopping experience."
Last week, Travelzoo US reported a summer mobile visit surge, with connected devices accounting for a quarter of total web traffic.