Portals do not remember each other. Every time you step through one, the game does a fresh search for a portal near where you should arrive — and if it finds someone else's, that is where you go.
The two rules that explain everything
One block in the Nether is eight blocks in the Overworld. Overworld coordinates are divided by eight going in, and multiplied by eight coming out.
On arrival, the game looks for an existing portal near the calculated destination. If it finds one within the search area, it uses it. If it does not, it builds a new one.
Coordinate conversion
| Overworld | Nether |
|---|---|
X 800, Z -400 | X 100, Z -50 |
X 1600, Z 1600 | X 200, Z 200 |
X 0, Z 0 | X 0, Z 0 |
| Y is not converted | Y stays roughly the same |
Building a pair that always links to each other
- Note the Overworld portal's coordinates
Press
F3and read X, Y and Z at the portal block itself, not from a distance. - Divide X and Z by eight
Round to whole numbers. That is where the Nether portal has to be.
- Build the Nether portal at those exact coordinates
Within a couple of blocks is fine. Twenty blocks off, and the game may find a different portal first.
- Test it both ways
Linking is calculated in each direction separately. A pair that works one way and not the other is normal and means one of the two is misplaced.
Because the Overworld is eight times larger, portals a thousand blocks apart in the Overworld are only 125 apart in the Nether — close enough for the search to grab the wrong one. This is why busy servers end up with everyone arriving at one person's base.
Build one tunnel network in the Nether with portals at deliberate coordinates, and have people connect to it rather than digging their own. It is the standard answer on multiplayer servers, and it also cuts the number of loaded chunks in the Nether considerably.
Walking through the Overworld portal puts you at your Nether portal, and walking back puts you where you started — five times in a row.