The Nether runs at an 8:1 scale to the Overworld — 1 block in the Nether equals 8 blocks in the Overworld. Type in either side.
Y (height) doesn't change between dimensions — only X and Z scale by 8. Nether Y is still capped by that dimension's build limits in survival.
Overworld-to-Nether conversion divides X and Z by 8 (rounded to the nearest block) per Minecraft's actual dimension scaling, while Y passes through unchanged since height doesn't rescale between dimensions; editing either side updates the other in real time, and the chunk display floors each coordinate divided by 16 (Minecraft's chunk size) to show both the Overworld and the corresponding Nether chunk for the same location.
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