iOS Resolution
This recommendation is based not on aesthetics — how the controls look — but on the size of human fingertips. That’s the real constraint. 44 points isn’t a magic number; it’s a by-product of the size of the pixels on the original 2007 iPhone display (pre-retina, one point equaled one pixel). On every iPhone to date, from the original through the 5S and 5C, there has been a single consistent point resolution: 163 points per inch. That means a 44 × 44 point UI element has remained exactly the same physical size (as measured in inches or millimeters).
The original iPad introduced a second point resolution: 132 points per inch. This has remained consistent on the large (9.7 inch) iPads. The iPad Mini (both original and retina) uses the iPhone’s 163 points-per-inch resolution. Apple’s recommended target sizes did not change for the 9.7-inch iPad: they simply made the recommended tap targets physically larger. 44 points on an iPhone or iPad Mini is roughly 0.27 inches (6.9 mm). 44 points on a 9.7-inch iPad is 0.33 inches (8.4 mm). Everything is bigger by a factor of about 1.24.
