What are the screen dimensions of the iPhone 4s and iPhone 5s?
This can be easily calculated with the available information. Since screen dimensions are always specified as the diagonal measurement, the rectangle can be divided into two equal right-angled triangles, with the hypotenuse being the diagonal measurement and the aspect ratio of the display providing inputs for the calculation of the height and width.

iPhone 4S  


Display size (always specified as the diagonal size): 3.5 inches or 89 mm
Aspect ratio: 1.5 (which is specified as 3:2 and can be calculated from the resolution - 960 x 640 pixels; 960/640 = 1.5)
Calculating the height and width when the ratio of the sides and the length of the hypotenuse are known can be done manually or even quicker, by using WolframAlpha.
Check this calculation link for iPhone 4S on WolframAlpha. The result is 74.05 mm by 49.37 mm.


iPhone 5s  


Display size (always specified as the diagonal size): 4 inches or 100 mm
Aspect ratio: 1.775 (which is specified as 16:9 and can be calculated from the resolution - 1136 x 640 pixels; 1136/640 = 1.775)
Calculating the height and width when the ratio of the sides and the length of the hypotenuse are known can be done manually or even quicker, by using WolframAlpha.
Check this calculation link for iPhone 5s on WolframAlpha. The result is 87.12 mm by 49.08 mm.