Apple doesn’t provide the exact display sizes, as far as I know. You can calculate them though, since we have the aspect ratio (16:9). (Bear with me, math was not my strongest subject!)

It follows:

x = diagonal / √(16^2 + 9^2)

h = x * 16

w = x * 9

iPhone 5: 8.86 cm * 4.98 cm = 44.11 cm^2

iPhone 6: 10.4 cm * 5.85 cm = 60.90 cm^2

iPhone 6+: 12.18 cm * 6.85 cm = 83.39 cm^2

The difference in %:

iPhone 6 to iPhone 5: 38%

iPhone 6+ to iPhone 5: 89%

iPhone 6+ to iPhone 6: 37%

I hope I didn’t embarrass myself now.