Minecraft wiki entry for Historical_effects, associated text: Past X/Z: 268,435,456, a single unit of redstone dust renders large enough to cover four chunks at a time, and beyond X/Z: 1,073,741,824, will appear as large as 128 blocks wide. For a redstone dot, this would result in a single pixel being 128/6 = 64/3 = 21.3333333333333... blocks wide.