Work out the odds
A fire block ticks every 30 to 39 game ticks, so about 1.73 seconds. The catch chance is for an air block touching this one, at the same height as the fire; four blocks up it is a hundredth of that, which is why fire climbs a wall far more slowly than it crosses a floor.
Set fire to something
One layer, seen from above, which is the floor case. Paint a material, press Light it and click, then let it burn. Fire climbing a wall is a different question: four blocks up the spread rate is five times worse, and there is no up here.
208 blocks that burn
Showing the first 120. Search to narrow it down.
The pair that surprises everyone
Wool ignites at 30 and burns at 60. Carpet, made from the same wool, ignites at 60 and burns at 20. Carpet catches fire twice as readily and then sits there burning three times longer, which is why a carpeted floor carries a fire across a room that a wool one would not.
Hay bales are the other trap at 60 and 20, and leaves at 30 and 60 are why a forest fire moves through the canopy rather than along the ground. Planks and logs, the things people actually build with, are a sedate 5 and 20: a wooden house is far less flammable than the wool carpet inside it.
Where the numbers come from
FireBlock sets both values for every block in code rather than in a data file, which is why no wiki page carries them together. These are read straight out of that class, including the two loops that cover all sixteen wools and all sixteen carpets, and the formulas below the table are the ones the fire tick actually runs.
Frequently Asked Questions
What is the difference between ignite odds and burn odds?
Ignite odds decide how readily fire appears in an air block next to yours. Burn odds decide how readily your block is destroyed once fire is beside it. They move independently, which is why carpet catches twice as easily as wool and then survives three times longer.
Does difficulty change how fast fire spreads?
Yes. The spread chance is the ignite odds plus 40 plus seven times the difficulty id, divided by the fire's age plus 30. Hard adds 21 to the top of that fraction where Peaceful adds nothing, so a hard world spreads fire noticeably faster from the same materials.
Why does fire go out on its own sometimes?
Fire ages every tick, and the older it is the lower its spread chance, because the age is on the bottom of the fraction. At age 15 with nothing burnable underneath it, a fire has a one in four chance of going out on each tick. Rain kills it faster still.
How do I stop fire spreading through my build?
Leave a gap or use something that is not on this list. Fire checks a three by three column from one block below to four above, so a one block air gap will not save a wooden wall, but any non flammable block in the path will: fire cannot appear in air unless one of the six blocks touching that air is flammable.
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