It is a known fact that iPad is evolving as a key revenue generator for Apple. But, analysts say that even iPad covers could be contributing millions of revenue to Apple.

In the following graphs, let's explore the beneficial impact of iPad covers for Apple.

We think iPad covers could add $300 million of revenue in the June quarter, and perhaps as much as $150 million in gross profit. Hence, we think the most relevant color for iPads is green, BMO Capital Markets analyst Keith Bachman wrote in a recent note to clients.

Bachman believes there is a very high correlation between sales of iPads and sales of Apple's iPad covers.

With a sales price of approximately $40 a unit, and likely 50 percent gross margins, the analyst believe that iPads can provide a lift on average selling prices and gross margins.

If we assume that 90 percent of iPad sales in the June quarter include Apple's covers, then this would add about $300 million in revenue and $150 million in gross profit, or 60 basis points (bp) to gross margin, Bachman said.

For the third quarter ended June, the analyst expects Apple to ship 8.5 million iPads, and raised its iPad estimates for the fourth quarter to 9.5 million from 9.0 million.

Apple is expected to report its third-quarter results on July 19. Wall Street expects Apple to earn $5.80 a share on revenue of $24.92 billion, according to analysts polled by Thomson Reuters.