How font sizes at iPhone 6/6+ compare to earlier iPhones?

How font size is different in iPhone 6 / 6 Plus as compared to earlier iPhones (e.g. 5S)--given both the different screen size and DPI?

1. Did the perceived* font sizes in system interfaces and built-in apps grow proportionally with screen size?

   [*] Perceived--i.e. as measured in milimeters/inches, not in pixels.

2. What are Apple's guidelines for app developers in terms of font sizes for 6/6+ as compared to earlier iPhones? How strictly are they enforced via app moderation (or any other means)? Should all apps effectively demonstrate the same font size for similar UI elements, or they are allowed to decide on the size individually? Should DisplayZoom and Dynamic Type be strictly supported by every app developer?

The reason I'm asking is that with iPhone 4 I struggle with a small font in most of the apps I use--so curious whether it will change if I switch to iPhone 6/+.

Above all, text must be legible. If users can’t read the words in your app, it doesn’t matter how beautiful the typography is. When you adopt Dynamic Type in your app, you get:

• Automatic adjustments to letter spacing and line height for every font size
• The ability to specify different text styles for semantically distinct blocks of text, such as Body, Footnote, or Headline
• Text that responds appropriately to changes the user makes to text-size settings (including accessibility text sizes)

Make sure all styles of a custom font are legible at different sizes. One way to do this is to emulate some of the ways iOS displays font styles at different text sizes. For example:

• Text should never be smaller than 11 points, even when the user chooses the extra-small text size. For comparison, the body style uses a font size of 17 points at the large size, which is the default text-size setting.
• In general, font size and leading values differ by one point per text-size setting. Exceptions to this are the two caption styles, which use the same font size, leading, and tracking at the extra-small, small, and medium settings.
• At the smallest three text sizes, tracking values are relatively large; at the largest three text sizes, tracking values are relatively tight.
• The headline and body styles use the same font size. To distinguish it from the body style, the headline style uses a heavier weight.
• Text in a navigation controller uses the same font size that body style text uses for the large setting (specifically, 17 points).
• Text always uses either regular or medium weight; it doesn’t use light or bold.

iOS Human Interface Guidelines: Color and Typography

The answer is Yes and No, depending on the app developers. I purchased iPhone 6 Plus for the hope that I can see bigger text. But apparently, not every user or developer thinks the same.

On my iPhone 6 Plus, I turned on the "Zoom" mode in "Display & Brightness" for my aging eyesight. What it does is to render the text bigger. It works very well in Apple's own apps. The fonts are large and crystal clear. But when it comes to third-party apps, it is a mixed bag. There are some apps that are optimized for 6/6+ that render fonts beautifully and in large-enough sizes. But there are a majority of others (alas) that claim to be 6/6+ optimized but effectively make the rendered font almost 50% smaller than before the update. For example, 1Password, Flipboard and Pocket rendered fonts much smaller after the update. I regretted the updates and have contacted the app developers. On the other hand, the iCab Mobile browser rendered fonts as it should, comparable to Apple's own apps.

Now when I see the app developers release any 6/6+ optimized updates, I always take it with a grain of salt. A lot of them just change the resolution settings, put in higher-resolution graphics and call it an optimization. What they don't realize is that many people who buy these larger iPhones are expecting to use the bigger screen real estate to see bigger fonts, and the app developers need to tweak the app layout and design to achieve that. Some of the third-party so-called "optimized" apps display a lot of white spaces in their app now that the screen is bigger and their app is still using small fonts. For me, that is just stupid. Why I am buying a premium phone with a gigantic screen just to stare at white spaces? The app developers need to utilize that space for some useful purposes. I know some people would argue that they want to see more content and they prefer small fonts, but for my eyesight, a bigger font is not just a preference, it is a requirement. At least I want my apps to give me the option to increase font sizes. Or at the very least, these apps need to honor the global font settings that I made on my iPhone.