I add things in my head:
8
16
32
64
128
256
512
2048
4096
that's as far as I usually go in my head.
I hardly ever see textures that do not follow this .DDS or other formats like .PNG or .BMP. Usually you will see textures from 128 up to 4096, this is from my level editing and 3DS Max experience and of course every good game has a mod for 4K or 8K parallax texture pack but never 6K, but yeah it follows the byte formula. I have used Hammer editor for Day of Defeat Source a long time ago and It was strict on multiples of 2, meaning no 320 or 768, I had to use the above formula for textures when I was making a level for Day of Defeat Source that Steam conveniently wiped from my hard drive after hundreds of hours of editing, bastards. I had to use 64,128, 256, 512, 1024 or 2048 so this is where I got the multiples of 2 thing at.