Ideally texture sizes should be powers of two on the sides. These sizes are as follows: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 or 2048 pixels. The textures do not have to be square, i.e. width can be different from height.It is possible to use other (non power of two) texture sizes with Unity. Non power of two texture sizes work best when used on GUI Textures, however if used on anything else they will be converted to an uncompressed RGBA 32 bit format. That means they will take up more video memory (compared to PVRT(iOS)/DXT(Desktop) compressed textures), will be slower to load and slower to render (if you are on iOS mode). In general you'll use non power of two sizes only for GUI purposes.Non power of two texture assets can be scaled up at import time using the Non Power of 2 option in the advanced texture type in the import settings. Unity will scale texture contents as requested, and in the game they will behave just like any other texture, so they can still be compressed and very fast to load.One potential problem with using non power of two textures this is that Unity will convert these textures internally to power of two, and this stretching process can introduce minor visual artefacts.