You need 10–14 obsidian blocks for a Nether portal in Minecraft, depending on whether you include the corners.

Quick Scoop: How many obsidian for a portal?

For a functional Nether portal, the game only checks that there is a valid rectangular obsidian frame around a 2×3 (or bigger) opening.

  • Minimum obsidian (no corners):
    • 10 obsidian blocks.
    • Frame is 4×5 on the outside, with a 2×3 opening inside.
  • “Full” rectangle (with corners):
    • 14 obsidian blocks.
    • Same size, but all four corners are also obsidian.

Think of it like this: you’re building a doorway where only the sides and the “top” and “bottom” matter for the magic to work; the corner decorations are just extra flair, not required for activation.

Simple layout example

Imagine your portal from the front:

  • Height: 5 blocks total (outer frame), with 3 blocks of empty space in the middle.
  • Width: 4 blocks total (outer frame), with 2 blocks of empty space in the middle.

Using 10 obsidian :

  • Bottom: 4 obsidian.
  • Each side: 3 obsidian (6 total).
  • Corners are missing/filled with something else or just air.

Using 14 obsidian :

  • Same as above, plus 4 corner blocks to complete the rectangle.

Extra notes for your build

  • Larger portals are possible (up to 23×23 frame), which simply use more obsidian but don’t change the basic rule: 10 is still the smallest you need.
  • In survival, most players go for the 10-obsidian design to save time mining, then light it with flint and steel to activate.

TL;DR: how many obsidian for a portal?
Minimum 10 (no corners), 14 if you want the full framed look.

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