The rumors are getting louder that InvenSense (NYSE:INVN) will get its MEMS chips into the next Apple (NASDAQ:AAPL) iPhone. Rival STMicroelectronics (NYSE:STM) lost the accelerometer slot last year, and Apple may be looking to replace its gyroscope this year. Granted, these are still just rumors, but all indications are that InvenSense expects a big customer in the second half of the year.

How much would a design win in the iPhone 6 be worth to InvenSense?

What about iPhone 6 sales?
Just about every analyst thinks iPhone 6 sales are going to be "strong." Estimates range from 45 million units to 80 million units sold in 2014 alone.

Those estimates seem very high considering Apple sold a total of 51 million iPhones in its first quarter this year. CIRP estimates that 59% of those units were the newest 5s, or just over 30 million.

This year, Apple has the advantage of a contract with China Mobile at launch as well as the potential for a larger screen to draw more buyers. A recent survey showed that 35% of consumers planning on purchasing a new smartphone would be swayed to purchase an iPhone if Apple offered a larger screen model. Only 26% of respondents said they'd be willing to pay a $100 premium for a larger screen, though.

So, 45 million isn't completely out of the question. If the momentum carries over into subsequent quarters, InvenSense could easily fulfill 80 million units by the end of its fiscal year in March.

How much is a design win worth?
The value of an Apple design win depends on which socket InvenSense takes.

STM looks to be on the fray as an Apple supplier. It lost the accelerometer socket to Bosch last year in the iPhone 5s, but it held onto the gyroscope spot. InvenSense has a good chance of taking the gyroscope socket from STM in the iPhone 6.

InvenSense also makes a 6-axis (gyroscope and accelerometer combined) sensor that has made its way into other high end smartphones. Management has built up inventory over the last two quarters with silicon wafers that support its 6-axis chips. Considering 6-axis chips account for over 70% of InvenSense's units shipped, it may just be stockpiling to make room for whatever design Apple wants from it.

To stay conservative, I'll assume that if InvenSense wins a socket, it will be the gyroscope. I'll also conservatively price the gyroscope unit at $0.70. The result is a potential $56 million boost to InvenSense's top line in fiscal 2015. It would see a further increase in fiscal 2016 with a full year of iPhone 6 sales, and as Apple phases out old iPhone models.

InvenSense already expects to increase revenue 25% to 35% in fiscal 2015 without the aid of any new design wins. The iPhone 6 design win could boost revenue an additional 20% to 30%. Currently, analysts are estimating InvenSense to increase revenue 28.6% this year.

For STMicroelectronics, a loss of the gyroscope socket to InvenSense will be just another in a long slow, decline of MEMS design wins for the company. It would represent a significant loss of revenue, but the company's Analog & MEMS segment accounted for $1.3 billion in sales last year, significantly higher than InvenSense's $252 million in total revenue.

Still, STM's MEMS division continues to experience a decline in revenue and market share, and another loss at Apple will put even more pressure on the segment.

In it to win it
Although analysts continue to upgrade InvenSense, stating their beliefs that the company won a design in the iPhone 6, their revenue estimates seem to disagree. As such, if the iPhone 6 does include an InvenSense chip, there's significantly more upside to the stock price than current estimates imply.

On the flip side, the low estimates imply not much Apple speculation is built into the current stock price. This lowers the risk of investing in the company today. If it turns out InvenSense doesn't win a design in the new iPhone, the stock price will likely go down, but it should recover relatively easily.