The Apple iPhone 6 and iPhone 6 Plus, both have a 8-megapixel 1/3-inch sensor. This is the same sensor size as the iPhone 5S, but larger than the iPhone 5 which has a 1/3.2″ size sensor.
Let’s take a look at the sizes in millimeters:
iPhone 6 / 6 Plus sensor size: 1/3″ = 4.80 x 3.60 mm
iPhone 5 sensor size: 1/3.2″ = 4.54 x 3.42 mm
Let’s take a look at a side by side sensor size comparison illustration that shows you how big the iPhone 6 and iPhone 6 Plus sensor is versus other sensor types.
You can see that the Apple iPhone 6 / iPhone 6 Plus sensor (seen in black in the above image) is slightly larger than the iPhone 5, but significantly smaller than that of the Z3, Lumia 1020 and certainly much smaller than the Nokia 808 PureView.
This is how small or big (depends how you look at it), the iPhone 6 / 6 Plus sensor is compare to some other popular mobile phone image sensor sizes.
Check out the Apple iPhone 6 and iPhone 6 Plus size comparison here.