I'm making a standard 9x9x5 zombie spawner and there are numerous tutorials out there. I'm trying to figure out for myself how to improve the efficiency, because I feel something is wrong with my design.

When mobs are spawned, how far from the spawner do they need to go before the spawner can spawn again? According to wiki:

If, at the time of spawning, 6 or more mobs of the spawner's type are present within a 9×9×9 area, centered on the spawner block, the spawner "poofs" without creating any mobs and then waits for the next cycle.

Does that mean mobs must be just outside the 9x9 room?

This is how the tunnel looks like, which is supposed to get the mobs out as soon as possible:

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However I don't think it is working properly, because the zombies bunch up too much, and the little zombies block the elevator.

  • I suggest digging the whole room down a few blocks. Mob spawners can spawn mobs in mid-air, and they'll immediately fall out of the "restricted" area, so the bunching up is not limiting your rates.
    – MrLemon
    Commented Dec 21, 2015 at 13:04

2 Answers 2


Your water elevator is misconfigured. It looks like it is flowing from under the sign, INTO your room. That is going to cause the bunching you are witnessing. I assume you are not seeing any zombies go up your water elevator.

Here's a 3 step process to make sure things are working well:

  1. Make sure mobs are going up your elevator (or following whatever exit route you have designed.)
  2. Make sure you have not reached the "local" mob cap. That is, the number of mobs in a 9x9x9 region around the spawner is < 6.
  3. Make sure your global mob cap is not getting reached. The Spawn article on the Wiki explains this. Basically it's "Video Rendering Radius"^2 * 70 / 289. So, by default on single player this is around 70 hostile mobs.

One way to ensure 2 is to dig the floor down deeper than you have, cover it in water, and the mobs will immediately fall out of the way.


It can be eather that:

there are too many mobs in the world at that moment and the game can't support the many entities at the time. (It needs a safe range of entities so the sistem does not crash do to the many individual forms mooving around)

OR, yes. There can be too many mobs at the spawn area and there's not enough room to spawn anything. So you'll have to make a sistem to move the mobs to a far away location to make room to spawn.

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