Rust furnace calculator

How smelting works now

Furnaces in Rust run at a fixed speed. There was a time when splitting your ore into many small stacks made a furnace faster, and plenty of old guides still say so, but that has been gone since 2023. Today the only things that matter are the furnace type, the ore type and how many furnaces you spread the ore across.

A small furnace smelts 0.3 metal ore per second. A large furnace does five times that, 1.5 per second, and an electric furnace sits in between at 0.5 per second while costing no wood at all. Sulfur ore smelts twice as fast as metal ore in every furnace, and high quality metal ore smelts at half the speed. The calculator assumes the ore types go through one after another, which is what happens when you fill every slot and walk away.

Wood burns at half a wood per second in a small or large furnace, and every wood that burns has a three in four chance of leaving a lump of charcoal behind. That is why the charcoal figure is an average: 1,000 wood gives you about 750 charcoal, sometimes a little more, sometimes a little less. Electric furnaces need 3 power and give you no charcoal, so if you are making gunpowder you still need a fire somewhere.

Crude oil and the refinery

Crude oil does not go in a furnace. It goes in a Small Oil Refinery, which turns one crude into three low grade fuel and burns wood doing it, a bit faster than a furnace does. Add crude to the calculator and it works out the refinery time and wood separately, then shows whichever run finishes last as your total time.

Planning a smelt

A large furnace takes about 11 minutes for 1,000 metal ore and burns roughly 333 wood doing it, so a full night of farming is usually an hour or two of furnace time. Spread the ore across several furnaces and the time divides by the count while the wood stays the same. If you are smelting sulfur for a raid, run the result through the crafting calculator to see how much of the charcoal you can keep for gunpowder, and the raid calculator to see what that sulfur buys you.