What next?
Smelting is the middle of a build, not the end. Here is the rest of the chain, from planning the shape to powering it.
What your result means
Fuel needed is how many units of your chosen fuel the job takes, always rounded up — you cannot burn most of a piece of coal. Total smelting time assumes one furnace at the standard ten seconds per item; time in parallel divides the queue across the furnaces you actually have, which is the only way to make a large job finish in a session. Wasted fuel capacity is the part of the final unit that burns empty — small for coal, large for a lava bucket on a short job, and the reason the cheapest fuel by count is not always the right choice.
Why this one is different
Total time is given twice: as one furnace working through the queue, and as the same queue split across however many furnaces you have running. Fuel needed comes with the capacity you will waste on a partly used piece, and the cheapest fuel for the job is named rather than assumed to be coal.
A lava bucket smelts 100 items — and wastes most of that on a stack of 64
Fuel is ranked by how many items each unit smelts: bamboo a quarter of one, planks one and a half, coal eight, a blaze rod twelve, dried kelp blocks twenty, a block of coal eighty, a lava bucket a hundred. On a big job the ranking is exactly right and lava is unbeatable.
On a small job it inverts. Smelting a single stack of 64 with a lava bucket burns capacity for 36 items you do not have, and the bucket is gone. Coal takes eight units and wastes nothing. The efficient choice depends on the size of the job, not on the fuel alone — which is what the wasted-capacity figure above is for.
How it works
A furnace smelts one item every 200 game ticks, which is 10 seconds at the normal tick rate, and that time is the same for every recipe. Each fuel has a burn time also measured in ticks, so dividing its burn time by 200 gives the number of items it can smelt: coal burns for 1,600 ticks and therefore smelts 8 items. The fuel requirement is the item count divided by that figure and rounded up, since a partly used unit is still consumed. Running several furnaces divides the queue but not the per-item time — four furnaces finish four times sooner because they work simultaneously, not because each is faster.
How to use this calculator
- Enter the number of items to smelt. A stack is 64, and a full double chest of ore is 3,456.
- Pick your fuel. The item count each one smelts is shown in the list.
- Set how many furnaces you will run at once to see the real finishing time.
- Check the wasted capacity row before committing a lava bucket or a coal block to a small job — a cheaper fuel is often the better fit.
Formula
items per fuel = that fuel’s burn time in ticks ÷ 200, since one smelt takes 200 ticks. Coal burns 1,600 ticks, so it smelts 8. The ceiling on the fuel count is because a partly consumed unit is still used up. Time in parallel assumes the queue splits evenly across furnaces.
Example calculation
Smelting 384 raw iron — six stacks — with coal:
Time = 384 × 10 = 3,840 seconds = 64 minutes in one furnace
Across 8 furnaces = 48 items each = 480 s = 8 minutes
Same job with lava buckets = ⌈384 ÷ 100⌉ = 4 buckets, wasting 16 items of capacity
With dried kelp blocks = ⌈384 ÷ 20⌉ = 20 blocks, an exact fit
An hour in one furnace is the figure that surprises people, and it is why bulk smelting is a furnace-array problem rather than a fuel problem. Eight furnaces turn the same job into eight minutes for the same 48 coal.
Frequently asked questions
How long does one item take to smelt?＋
Ten seconds in a standard furnace, or 200 game ticks, and it is the same for every recipe — ore, food, sand and clay all take the same time. A blast furnace and a smoker each halve that to five seconds, but only for the items they accept: ores and metal for the blast furnace, food for the smoker. Nothing speeds up a standard furnace.
Which fuel is the most efficient?＋
By items smelted per unit, a lava bucket at 100 is the highest, followed by a block of coal at 80 and dried kelp blocks at 20. But efficiency per unit only matters if you can use the whole unit — on a job smaller than the fuel’s capacity the surplus burns with an empty furnace. For renewable bulk smelting, dried kelp blocks and bamboo are the usual choices because both farm easily; coal is the practical default for anything mid-sized.
Does the furnace waste fuel if I stop early?＋
Yes. Once a fuel unit starts burning it burns to completion whether or not there is anything left to smelt, and the remaining burn time is lost when the furnace empties. Feeding the input slot before the last unit finishes is the way to avoid it, which matters most with high-capacity fuels like lava and coal blocks.
Do blast furnaces change the fuel needed?＋
They halve the time per item but not the fuel per item, so the fuel count stays the same while the job finishes twice as fast. This tool uses the standard furnace rate of ten seconds; halve the time figures for a blast furnace or smoker, and leave the fuel figures alone.
How many furnaces should I build?＋
Enough that the job fits the time you have — the parallel row above answers it directly. A common arrangement is eight or sixteen fed by a hopper line from a chest, which turns an hour-long stack of smelting into a few minutes. Beyond that the constraint is usually fuel supply and item throughput rather than furnace count.
Is bamboo really worth using as fuel?＋
Only in volume, and only because it is trivially automatic. One bamboo smelts a quarter of an item, so it takes four just to smelt one — but a bamboo farm produces it endlessly with no input, so the poor per-unit figure stops mattering. It is the clearest case of the ranking above being the wrong way to choose.
Related calculators
Assumptions & limitations
Every figure here comes from a simplified model. Keep these limits in mind when reading your result:
- Assumes a standard furnace at 200 ticks — ten seconds — per item. Blast furnaces and smokers halve the time for the items they accept; the fuel count is unaffected.
- Assumes the game is running at the normal 20 ticks per second. Server lag lengthens real elapsed time without changing the tick figures.
- Fuel counts round up, because a partly consumed unit is still spent. The wasted-capacity row shows how much of the last unit burns with nothing to smelt.
- Parallel time assumes the queue divides evenly across furnaces and that each is kept supplied. In practice a hopper line adds a small delay and an unattended array will idle.
- Burn times are those of current Java Edition. Bedrock matches on the fuels listed here, but values have changed between versions and could change again.
- Does not account for experience gained, item stacking limits in hoppers, or the time to build and load the array itself.