Two Nether portals will usually stop auto‑linking once they’re outside the game’s “search radius” for an existing portal, which is 128 blocks in the target dimension’s coordinates.

Core rule (Java & Bedrock, modern versions)

When you enter a portal:

  1. The game converts your coordinates to the other dimension
    • Overworld → Nether: divide X and Z by 8
    • Nether → Overworld: multiply X and Z by 8
  1. It then looks for the closest existing portal within a 128‑block radius (spherical/box search) of that target spot.
  1. If it finds one, it links you to it; if it doesn’t, it creates a new portal there (or as close as it can).

Because of the 8:1 scale:

  • Two Overworld portals closer than ~1024 blocks apart in X/Z often end up mapping to almost the same place in the Nether (1024 / 8 = 128), so they usually share a Nether portal unless you manually set things up.
  • Two Nether portals closer than ~128 blocks apart in X/Z often map back to the same Overworld portal for the same reason, just reversed.

So as a rough, safe rule of thumb:

  • Overworld portals should be more than 1024 blocks apart (in both X and Z) if you want the game to be “forced” to use different Nether portals on its own.
  • Nether portals should be more than 128 blocks apart (in both X and Z) to reliably avoid sharing one Overworld portal.

“But I’ve had portals closer that don’t link?”

That’s because once you manually link portals with correct coordinates, the distance rule becomes less strict.

You can:

  • Take your Overworld portal’s X/Z, divide by 8, and place the Nether portal exactly there (ignoring Y).
  • Do this for both ends of each pair.
  • When portals are precisely matched this way, you can have them very close together , even a few blocks apart, and they’ll still link correctly because each one is closer to its intended match than to any other.

That’s also why players sometimes build two Nether portals side by side that go to different Overworld portals: each Overworld portal’s converted coordinates land slightly closer to one Nether frame than the other.

Practical distances to use

If your goal is “I just don’t want these two to ever connect by accident” and you don’t want to think too hard:

  • In the Overworld
    • Make portals at least 1024 blocks apart in X and/or Z.
    • This pushes them outside each other’s shared 128‑block Nether search radius.
  • In the Nether
    • Keep portals at least 128 blocks apart in X and/or Z.
    • That keeps their mapped Overworld positions from overlapping search areas as well.

If you’re okay with a bit of math and want tighter spacing, the trick is to:

  • Align coordinates exactly (divide/multiply by 8).
  • Make sure each portal pair is clearly closer to its own partner than to any others.

Tiny example story

Imagine you have a home base at Overworld (0,0)(0,0)(0,0) and a village at (800,0)(800,0)(800,0).

  • Home portal maps to Nether (0,0)(0,0)(0,0).
  • Village portal maps to Nether (100,0)(100,0)(100,0).

Those two Nether spots are only 100 blocks apart, which is less than 128 , so if you let the game auto‑create portals, you might end up with both Overworld portals using just one Nether frame when the first one is built.

But if you:

  • Manually place a Nether portal exactly at (0,0)(0,0)(0,0) for home, and
  • Another exactly at (100,0)(100,0)(100,0) for the village,

then each Overworld portal will reliably find its own Nether counterpart, even though they’re within the 128‑block radius, because the “closest portal” rule now clearly favors the correct one.

Information gathered from public forums or data available on the internet and portrayed here.