TexturePacker
Memory = Color Depth x width x height
Color Depth is normally 32 bit, which is 4 bytes
If width = 128, and height is 128,
Memory would be 4 x 128 x 128 = 65536 Bytes, or 65 kB
Tutorials
How to use TexturePacker to create a sprite sheet
SpriteSheets - The Movie Part 1
Lighting a whole Pixel Art Town at Night in Unity - Tutorial, Part 1: Lots of Streetlights
NodeJS Module: https://github.com/odrick/free-tex-packer-core