Apple could soon add an iWatch to this product lineup, but how will that help its bottom line? Source: Apple.

In case you haven't heard, many are expecting a little something called the Apple (AAPL -2.88%) iWatch to debut this coming fall. As usual, Apple hasn't spilled the beans on such a device, but rising competition in the wearable tech space and recent moves by Apple all point to such a device.

So, if the iWatch is coming, how much can investors expect Apple to make from the device once it goes on sale? To help answer that, we gathered up a handful of analyst estimates to see what they had to say.

Let's take a quick look.

Analyst

First-Year Unit Sale Projection

Cost of Device

iWatch Revenue Estimate

Gene Munster (Piper Jaffray)

5 million to
10 million

$350

$1.75 billion to 3.5 billion

Toni Sacconaghi 
(Sanford C. Bernstein)

9 million to
25 million

$250

$3.4 billion to
$5.7 billion

Katy Huberty
(Morgan Stanley)

32 million to
58.5 million

$299

$17.5 billion

Steven Milunovich
(UBS)

21 million

$300

$6.5 billion

First of all, these are some wide-ranging estimates, even if you look at just one analyst alone. Some are basing their projections on what percentage of iPhone owners will become iWatch buyers, and thus the numbers fluctuate. But all of this means we still have a cloudy view of how much Apple could benefit from a wearable device. Should we expect $1.75 billion in revenue or $17 billion? It's a huge gap.

I hate to say it but...
No one has a clue. While these may be educated guesses, the sheer difference in unit sales means the analysts clearly don't know how many iWatches Apple is going to sell. The truth is, the wearable tech market is still unproven. Google only recently opened Glass sales to everyone in the U.S., and Samsung -- while firmly in wearables -- can't quite be considered a success story. This is uncharted territory for Apple and many other tech companies. That doesn't mean the highest iWatch estimates are off base, but rather that it's hard to guess how many devices Apple could sell when the company's never even ventured into this segment before.

Take for example Wall Street's sales estimates for the iPad before its debut. The range of first-year sales were from 1.1 million to 7 million, according to an All Things D article from three years ago. So, how many iPads did Apple actually sell in 2010? Nearly 15 million -- double the amount of the most liberal estimates.

Let everyone guess how many iWatches Apple will sell. I suppose when the estimates range from 5 million to 58 million, someone will be able to claim they were right. But as the iPad proved a few years ago, everyone's just throwing out numbers.