# How does Height play into hostile mob spawns?

The Minecraft Wiki Spawn page goes into great detail about how hostile mobs spawn. But it omits details about how height plays into common spawns. It DOES mention how slimes require the chunks they spawn in to be at a certain height level, but I'm more concerned with how the rest of the common hostile mobs spawn. (Namely Zombies, Creepers, Skeletons and Spiders)

To clarify a bit:

Mobs spawn naturally within a 15x15 chunk (240x240 block) area around the player.

Ok, well, thats simple enough, one chunk is a 16x16 block centered on the player, got it. But, thats a two dimensional measurement, and this is a VERY three dimensional game. Is height irrelavent in such spawning mathmatics? If so, wouldn't that mean that I could be at sea level, with a dark cavern at bedrock beneath me, and have some of the mobs I want to slay spawn all the way at bedrock rather than at the same height I am?

Or even more prevalent, (and the main reason behind the question reveals itself) I have a monster grinding tower that I've built. The tower currently has 6 floors with each floor boasting a 2 block high space for the mobs to spawn in. If you include an extra block for the actual 'floor' of each level of the tower, that makes 18 blocks high. Now if I'm near enough and far enough (as the reqs require for spawning) to and from from the tower for mobs to spawn inside of it, how (if at all) will the different high levels of the tower affect my spawn rates inside each floor?

I know that this question was asked a long time ago, but just thought I'd give an update and a correction for future people that read this. (please consider that things may also change in future)

Ok, so first of all, you mentioned that a Chunk is 16x16 block around the player. This is incorrect. A chunk is a section of the terrain and is nothing to do with where the player is. The chunk does not move. A chunk is a 16x16x256 (W,D,H). So for the mob spawning. The quote you gave is correct, however, does not note that it is centred around the chunk that the player is standing on. So 7 chunks in every direction from the border of the chunk you are standing in.

And now for your question :) Recently, (not sure when it started) height has become even more important for mob spawning and each chunk is split into segments. This is to reduce the amount the game has to render and does this by going up in 16 block segments starting from 1. So 17, 33, 49, etc. This is called the lc value and can be shown on the debug screen (F3). It is important for mob spawning, why? Because any segments in the chunk above the maximum segment that has anything other than air in do not get checked for spawning conditions. This therefore means that there are many less blocks to check which in theory will make your mob grinder or xp farm more efficient.

There is a fair amount more... however, I think this answers what you wanted. At least I hope it does ;) Best of luck guys.

• The original answer was posted before Anvil came out (which included these changes!). Thanks for the update, and welcome to the site! Nov 26, 2012 at 23:46
• Not that subchunks (the vertical slices of a chunk 16 blocks in size) are no longer used in 1.13+. See my answer.
– qwr
Nov 17, 2020 at 10:31
• This answer is woefully obsolete. Last shreds of valid information here went obsolete with Minecraft 1.13.
– SF.
Nov 17, 2020 at 11:32

Except for Slimes, height does not have an effect on mob spawning. Chunks are 16x256x16, and are loaded all at once. It is impossible for only part of a chunk to be loaded. So this means yes, it's possible for a mob to spawn near bedrock even if you're on the surface.

Note that this is not true for mob spawners. A mob spawner will only spawn a new mob if a player is within 16 blocks of it (calculated spherically).

• I really dislike your answer, not because you worded it wrongly but because you just confirmed something that will make my life extremely difficult. -.- Thanks for answering all the same though! lol. Jan 16, 2012 at 7:53
• @Ender: Yup, the chunk system adds some odd quirks like this that are unfortunately unavoidable. Hope you get it all worked out! Jan 16, 2012 at 8:27
• @Ender: This means, to get mobs to spawn in your tower, (and only your tower) you need to light or otherwise render inoperable mob spawning in the entire vertical extent of the chunk. Get your torches ready! I think you realized that but making the point explicit.
– John
Jan 16, 2012 at 20:18
• @John: It will if I dig directly beneath it to bedrock, light up areas i find under it, and retrospectivly only light up HALF of one of the chunks, then I'll have mobs spawning in the other half rather than in my tower. Jan 17, 2012 at 17:50
• The entire premise of this answer is wrong because chunk loading is distinct from mob spawning.
– qwr
Nov 17, 2020 at 10:41

The most important factors for mob spawning are the mob cap and the 128-block radius despawn sphere. The mob cap isn't relevant to this question other than the common knowledge fact that if hostile mobs fill the mob cap then no more will spawn. While mobs spawn in a 15x15 square of chunks centered on the player, they immediately despawn if they are not within 128 blocks from the nearest player, meaning mob spawning is effectively within a 128 block radius sphere around the player.

In 1.2.1, the max build height was raised from 127 to 255. This made building farms way up above the previous height limit, or just having the player AFK there, an attractive option. For example, if you built a mob farm in the sky at around y=90 and AFKed at y=200 or above over a relatively flat area, then the only mobs that would (effectively) spawn would be those in your mob farm, since your farm would be within 128 blocks but the mobs on the surface at about y=64 and below in unlit caves would be more than 128 blocks away and not affect the spawning rates. This saved a lot of tedious lighting up of areas and gave the crazy spawn rates similar to those in skyblock where mobs seems to spawn insanely fast (they had nowhere else to spawn). This concept still applies today to general purpose mob farms (not including mobs that only spawn in certain areas, such as slimes, witches, wither skeletons, etc.)

Nowadays (1.13+) to maximize rates as much as possible you want to build farms as close to y=0 as possible. In each chunk, for each x/z position, spawning depends on the topmost non-air block (from 1.8 - 1.13, this depended on subchunks and the highest non-daylight-transparent block so glass AFK platforms did not affect rates. This was changed in 1.14). The spawning base block is chosen randomly in a x/z position in the chunk and then randomly based on the max y level of non-air block, therefore building the farm as low as possible and ensuring there are only air blocks directly above spawning platforms maximizes spawning.

• This is essentially correct for 1.13-1.16, although the answer would benefit from mentions of the mob cap and the despawn sphere which tend to be the dominating factors ruling mob spawn frequency.
– SF.
Nov 17, 2020 at 11:39
• @SF. I've added explanation on some history and building farms at high y level.
– qwr
Nov 17, 2020 at 22:21
• Some small errors: "Blocks that are transparent such as glass don't affect spawning and can be used for AFK platforms." - they didn't pre 1.13. Currently every block, including transparent, intangible, liquid, everything but air raises the column height and decreases spawn rate in that column. Additionally, you don't need an empty perimeter to benefit from high spawn rates at low y-level; you only need empty space above the spawn platforms, the rest just must be spawn-proofed, e.g. lit up. (perimeter reduces lag though and helps against missing any spawnable spaces)
– SF.
Nov 17, 2020 at 22:36
• @SF. I thought it was only non-daylight-transparent blocks that affected spawning. I'll add the info about the perimeter.
– qwr
Nov 17, 2020 at 22:45
• That was the case for 1.12 and before (+ the whole subchunk deal). I'm not 100% sure about 1.13, but I'm sure about 1.14+.
– SF.
Nov 17, 2020 at 22:55