When word got out a few weeks ago that the white iPhone was slightly thicker than the black model, the Internet buzzed with concern, much of it sarcastic. After all, the reported difference in depth was just 0.2 millimeters, so small it was difficult to even measure. Could that tiny bit of extra girth actually make any practical difference whatsoever?
Probably not, but it still aims a spotlight—or rather a microscope—at the issue of design tolerances, or the margin of error allowed in the production of an electronic device. While a difference of 0.2 millimeters (or 0.008 inches) certainly sounds minute, in the world of cell phones, where the race to be the thinnest and lightest perhaps matters most, it could amount to about 2 percent of the overall thickness of a phone. Still not huge, but it doesn't sound as small put that way.
"Sizegate"
First, let's establish our facts. Reports of the white iPhone's added thickness first emerged from various buyers when the device went on sale at the end of April. Soon after the story appeared, Apple Senior Vice President Phil Schiller contradicted the reports on Twitter, saying the white iPhone 4 "is not thicker, don't believe all the junk that you read."
Using a caliper accurate to hundredths of a millimeter, PCMag measured both our white iPhone review unit and several black iPhones we had handy. Based on our measurements, the white iPhone is about 0.15 millimeters thicker than the black version.
Interestingly, there was some variance even among the black iPhones measured, though the difference wasn't as dramatic as between black and white. The black iPhone 4s we measured varied between 9.31mm and 9.35mm thick, whereas the white one clocked in at 9.47mm. Apple's spec page says the iPhone 4's thickness is 9.3mm, though it doesn't go more precise than tenths of a millimeter, and it also includes the caveat, "Actual size and weight vary by configuration and manufacturing process."
Vary by how much, though? And why the larger variance between the white and the black models? Does the added girth of the white iPhone 4 come from some different process that's used in making it, or could this just be a random mistake on the production lines?
Precision Is Everything
Almost certainly the former, says Oliver Duncan Seil, senior design director at Belkin, which manufacturers plenty of accessories for Apple's iPhone, iPad, and iPod lines, many of them cases. The machine tools used in today's factories are designed with extreme precision in mind, he says. Although the tolerance can vary depending on the size and nature of the part being built, no reputable factory could stay in business if the products coming off its product lines varied in size significantly.
"It's very rare that we see tolerance issues," he says. "For tooled products—the standard plastic stuff that you'd find—those steel tools are manufactured with very high-precision machinery, so you can get very tight tolerances. A tight tolerance would be in the range of a thousandth of an inch (0.001") or less."
Kyle Wiens, co-founder of the gadget teardown site iFixit, agrees. In his experience, "Design tolerances for most mobile devices is pretty tight. If you think about the methods that companies use to assemble devices and the actual sizes of things, moving an attachment point even 1mm can cause major fitment issues."
The precision of the tools involved is only one factor, of course. As Seil points out, parts of the production process—injection-molding, for example—involves heating and cooling individual plastic parts heating and cooling, which can also create variation in individual parts.
"You can have the most precise tool on the planet, but if the processing isn't perferct, then you will have products go out of tolerance after they're made," says Seil. "You can expect something that's not high-end to be made with a tolerance that's about the thickness of a hair, or about a tenth of a millimeter.
"We aim for less than that," he adds.
What could—and could not—have led to the white iPhone being thicker? Read on.
Does This Color Make My iPhone Look Fat?
If Belkin,a third-party accessory maker, is aiming for such tight tolerances, how then to explain the thicker white iPhone? One theory that Seil quickly shot down is that the paint is simply thicker. Since the opacity of white paint is less than black, you would have to coat something with more layers of white paint in order to get the same level of opacity as a black-painted version. However, a coat of paint is so thin, thinner than a human hair, he says, that it wouldn't account for anything more than a couple of thousands of a millimeter.
Clearly, the production and assembly of the white model must be different from the black, since the phone has been physically changed from the black. Japanese blog MacOtakara performed a teardown of the white iPhone, revealing a different camera sensor, and the casing has an extra slit near the top, ostensibly for a new proximity sensor. It's logical to conclude that those design modifications had the effect of making the device slightly thicker overall.
What Issue?
Is it really a problem, though? Sure, the white iPhone is thicker than the black one, but we're only talking about 0.2mm here. As far as Belkin is concerned, there's no issue. Seil says the company performed its own tests on multiple white iPhones and the testers concluded that they didn't have to make any adjustments to their product line. In other words, all their cases still fit.
"We've made an assessment of the situation very quickly, very diligently," says Seil. "Of course, it affects us greatly, and our assessment was that we don't have to fret. We feel confident that our products will fit for both phones. The difference was marginal."
Still, given how precise those manufacturing tools are, and assuming Apple's quality-assurance process is remotely competent, there's simply no way that Apple could not have known that the white phone had a slightly thicker shell than the black one. The question then becomes: Was the company obligated to tell its customers and vendors? Should they even have gone as far as creating a different designation ("iPhone 4a"?) for the white model?
"Do they need to tell us? No, they don't," Seil says. "They release the kind of information that they see fit. And all of us that are part of the ecosystem that we're very happy to be a part of—have to deal with the consequences. We're all playing by the same rules."
It's probable the Apple came to the same conclusion that Belkin did—that any extra thickness didn't have any practical effect—and decided not to say anything. Given that there haven't been any reports of people lining up to return cases they bought for their white iPhones, you could conclude (rightly) that a difference of 0.15 millimeters simply isn't a big deal after all.
Coming at it from the other way, though, if it really isn't a big deal, why doesn't Apple just admit that the white iPhone is slightly thicker, that it doesn't matter, and call it a day? It could be for a few reasons. Perhaps the increased thickness is limited to only a few production runs of the device. It's also possible Schiller didn't have all the information about the thickness of the white iPhone when he made his comments on Twitter. Or maybe Apple just sees no problem in declaring the white iPhone to have the same thickness as the black, even when there is evidence to the contrary.
Apple didn't respond to a request for comment. Maybe it doesn't need to; "Sizegate" certainly isn't on par with the iPhone 4's antenna problems that plagued the phone upon its initial release. But for anyone who's ever looked at a spec sheet as definitive, it's a reminder that every number cited is really just an average, and your mileage may vary. Sometimes a lot.