Minecraft wiki entry for Beginner%27s_guide, associated text: It takes 10 seconds for each item to be smelted. Different fuel items burn for different amounts of time; most items made from wood can be used as fuel, but coal or charcoal are more efficient, and other fuels may become available later in the game. Some common fuels: Any wooden tool (or sword) can smelt one item; a wooden plank can smelt 1.5 items (that is, 2 planks smelt 3 items, as shown above), and a piece of coal or charcoal smelts 8 items. Don't use logs directly as fuel; the log burns no longer than each of the four planks you could make from it.