It's old news that tablets are eating the lunch of old-line PC makers, but the size of the bites can be surprising. A series of reports last week showed PC shipments flat to down, while tablets – led by the iPad – are selling more strongly than most observers expected.

 

Let's start with the PCs. For the last seven quarters, global PC shipments have seen less than 10% growth, according to Gartner. In Q2 2012, PC shipments slipped to 87.5 million from 87.6 million in the same quarter of 2012. That's as small of a drop (0.1%) as analysts routinely measure, but even so, the numbers make it official: Making PCs is an industry in decline.

Meanwhile, sales of Apple's iPad are expected to easily surpass 11.8 million tally for Q1, thanks to the upgrade released in March. Among Wall Street analysts, the average estimate is 15 million iPads sold in Q2, according to Fortune. Among independent analysts – who have had a better track record of Apple forecasts recently – the average is 20 million. The highest estimate, 24 million iPads, comes from Asymco's Horace Dediu.

On Thursday, Charlie Wolf, an analyst at Needham and one of Wall Street's more respected tech analysts, raised his estimate for Q2 iPad sales to 20 million, in line with the independent analysts and up from his previous estimate of 13.5 million. What swayed Wolf was that the iPad was finding its way into businesses and organizations. Everyone, from the Baltimore Ravens to United Airlines to the Dutch Senate to Chinese high schools, is buying tablets.

If Wolf and others are right, it means that a little more than three years after the iPad debuted, one iPad is sold for every four PCs shipped. Thus, the iPad alone would account for 20% of the global personal computing market.

Considering that the iPad has a nearly two-thirds share of the global tablet market, a back-of-the-envelope calculation shows 30 million tablets and 88 million PCs shipped last quarter. That is, tablets could make up a quarter of the personal-computing market, if by “personal computing” we mean tablets and PCs are now one and the same industry. 

Who would consider tablets and PCs as a single industry? Microsoft, for one. The Surface device that the company announced last month was designed as a tablet-PC hybrid, just as Windows 8 was engineered as an OS for both form factors. Apple, of course, has been gradually making the same convergence for years. So even if research firms don't think of tablets and PCs as two sides of a coin, major players in hardware do.

So why not count tablets in the tally of PC shipments? It would certainly make the personal-computing industry look healthier. And it would show clearly how Apple dominates it. As Jim Dalrymple pointed out, Apple's share of this combined PC-tablet market would be substantial.

How substantial? Add 20 million iPads sold last quarter to the 4.5 million Macs analysts are expecting, and Apple is selling 24.5 million personal-computing devices, nearly double the 13 million PCs shipped by Hewlett-Packard.

And if Gartner's 88 million PCs figure were expanded to include an estimated 30 million tablets sold, then Apple's combined iPad and Mac sales would give it a 21% share of the market. HP's share would fall from 15% to something more like 11% and Dell's share would go from 11% to about 8%. Which sounds about right.

As Apple and Microsoft have indicated, for the purpose of analyzing the industry, the distinctions between the laptop and the tablet may have been useful in the past, but now it's as insignificant as the difference between a laptop and a desktop PC. It's time to start counting tablets and PCs together. Yes, break down the total into high-end ultrabooks and lower-cost laptops and tablets to offer more granular analysis, but let's see the big picture as well.