Minecraft wiki entry for Model, associated text: Using the "uv" compound, textures can be read from one file and parts of the file can be used for each side of the block. "uv" doesn't take the pixels of the file, it instead takes percentages of the file in terms of 16; for example taking the top half of a file uses "uv": [0,0, 16,8]: from the coordinates ([0% of 16], [0% of 16]) – (0,0) – which is the top-left pixel, and ends at ([100% of 16], [50% of 16]) – (16,8), which is the middle-right pixel. Because this works in percentages, resizing an image from 16×16 to 32×32, 64×64, etc., does not require changing the model file.