Apple is widely expected to introduce a smaller, cheaper version of its iPad on Tuesday, perhaps in response to the crop of 7-inch tablets that have popped up in the last year. But how are those tablets even doing anyway?

It turns out that the number of seven-inch tablets sold by each of Apple’s major competitors is small compared to the number of iPads it has sold.

To date, Apple has sold about 84 million iPads. Amazon’s Kindle Fire, the second-best-selling tablet, has sold about seven million units; Barnes and Noble has sold about five million Nook tablets; and Google has sold about three million Nexus 7 tablets, according to estimates by Forrester.

That’s about 15 million tablets across three companies. And while no single company presents a major threat to Apple yet, it’s not a number to sneeze at — after all, that’s 15 million more iPads that Apple could have sold. So it makes sense that the company is preparing its own smaller tablet at a lower price, said Sarah Rotman Epps, a Forrester analyst.

“Apple is smart to be acting before it gets to be more of a problem,” she said.

Steve Jobs once dismissed seven-inch tablets, saying they were “tweeners” that were too big to compete with a smartphone and too small to compete with an iPad. Several sources have said Apple’s smaller iPad will be 7.85 inches, which is a bit bigger than 7 inches but might still be considered a “tweener.” Would these sell nearly as well as the current iPad?

Stephen Baker, an analyst with the NPD Group, thinks smaller tablets are a viable category because they cater to people who don’t want to spend too much money on a tablet, or those who just want something smaller to carry with them everywhere.

Ms. Rotman Epps agreed. She said a 7.85-inch iPad could also broaden the product’s appeal to women because it would most likely fit in a purse.