HP retook the lead in the worldwide client computer market in Q1 2012, according to the latest figures published by analyst firm Canalys (http://www.canalys.com).

Apple had ousted the long-time market leader in Q4 2011, thanks largely to record iPad shipments (in excess of 15 million units). Canalys counts tablet sales among computer sales, though other research groups such as Gartner and IDC don’t.

In Q1, however, Apple shipped 11.8 million iPads, bringing its total client computer number for the quarter to 15.8 million. HP’s shipments were higher by around 40,000 units, according to Canalys estimates; just enough to give it the lead.

Lenovo took third place, with impressive year-on-year growth of 50%. Acer and Dell took the remaining top-five places, but with shipments down on the same quarter a year ago. The total client computer market grew by 21% to 107 million units.

While the tablet/pad category exhibited the highest growth — more than 200% year on year — notebook and desktop shipments were up too, rising 11% and 8% respectively. Netbook shipments, however, were down 34% on the year-ago quarter — the sixth such fall in succession.

“Most of the leading computer vendors have done a reasonable job of offsetting the declines in their netbook shipments over the past year with increased pad business,” says Canalys Research Analyst Tom Evans. “Samsung and Lenovo are two that stand out in terms of substantially increasing overall volume, though Asus has performed well too. The challenge is breaking out into the really big volumes to challenge the leaders — Apple and Amazon. So far, only Samsung has shown it can routinely ship more than a million pads a quarter.”

Globally, Canalys reports that pads represented 19% of all client computer shipments in Q1, up substantially from 7% a year ago, but down on the 22% recorded in Q4 2011. Netbooks have fallen to 5% from a high of 13% two years ago. Notebooks represented just under half of the overall market by units.