Considering a standard mob farm design, what's the minimum height I should build the spawning floor so that I'm sure I get 100% efficiency (no other mobs are counted toward the mob count cap)?

I don't feel like lighting up every cave yet, and I desperately need a working mob farm.

  • Are you asking how high the drop needs to be? – fraener Aug 17 '14 at 19:26
  • @fraener Nope. The way I kill the mobs is irrelevant in this question. Just at what level the spawning pads needs to be in order to avoid mobs in the underlying caves being counted towards the mob cap. – Shoe Aug 18 '14 at 9:38

This depends on many factors, including your position as a player and the type of terrain around you.

Mobs will despawn when they are out of a 128 block radius of the player.

This means that for the spawner to be active if the player is anywhere within 128 blocks at the spawner's level, it has to be at least 128 blocks above the ground. This works for pretty much any generic mob farm, and it works in a populated server. Having blocks in an area above level y128 can decrease efficiency of mob spawning, since it has to account for more chunks, though, so here are some other options:

If you want to make a less tall, but still efficient design you can locate the player above the farm so that the despawn radius includes the spawner but excludes the rest of the world. Note that this design is better suited for AFKing, since you will have to make many trips up and down for this to work. This can be used for witch farms, as well as hostile mob farms.

You can also "sanitize" a 128 radius area, by lighting up every cave and surface you can find. This is obviously quite tedious, but it can allow for a ground-level farm that is active no matter where the player is. This works for witch farms as well, and is probably your best efficiency if you are playing on a server.

  • Interesting. So I'd go Ground + 128 up and then AFK on top of the farm? – Shoe Aug 18 '14 at 9:43
  • You'd build a big tower that is greater than 128 blocks above the ground, then you'd stand on it. You would have the mob farm inside a 128 block radius of you, but the ground would be outside that radius. Any mobs that are on the ground will immediately despawn, but the mobs in the farm will not. Note that this might not work so well for an XP farm, I think you'd have to build an elevator that moves the mobs up to where you are (so they don't despawn after 30 seconds.) Here's a video that shows someone using this technique for a witch farm. youtube.com/watch?v=hj0YPPjticE – Aaa Aug 18 '14 at 17:29

If your concern is solely limited to other hostile mobs lowering your grinder's efficiency, then quoted from minecraft wiki,

Hostile mobs (and some others) that move farther than 128 blocks from the nearest player will soon despawn (see Despawning), so even with a larger chunk loading radius, the mob spawning area is more-or-less limited to spheres with a radius of 128 blocks, centered at each player.

What this means is that to get 100% efficiency, you should build 128 blocks above the tallest terrain you are at. ie 128 blocks about ground level.

  • I don't understand. Let's say the ground level is X; You are saying I should build the spawning pads at X + 128? Wouldn't that count mobs also down to X - 128 below and therefore lower the mob cap? – Shoe Aug 18 '14 at 9:40
  • @Jefffrey Any mobs that is 128 blocks away from you despawns thus, if you build it X + 128 high, and your player is at X + 128, the only valid location for mobs to spawn is your spawn platform – DarkDestry Aug 19 '14 at 16:25

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