VRAM tips
From Unify Community Wiki
Compression | Memory consumption
DXTC1 RGB: .5 Bpp (bytes/pixel)
DXTC3 RGBA: 1 Bpp
RGB 16bit: 2 Bpp
RGB 24bit: 4 Bpp
Alpha 8bit: 1 Bpp
RGBA 16bit: 2 Bpp
RGBA 32bit: 4 Bpp
To figure out total texture size: width * height * bpp
Add 33% if you have Mipmaps.