A Nether portal will not work just because the frame looks close enough. It needs a valid upright Obsidian frame and a fire-starting item before it opens to the Nether.
Start with the standard survival build, then use the alternate methods below if you are in Creative, fixing a Ruined Portal, casting obsidian with lava and water, or using commands.
Build the basic survival portal
This fixes the standard way to make a Nether portal from scratch in a normal Minecraft world.
Gather Obsidian for the frame.
Place two Obsidian blocks along the bottom of the portal opening.
Build three Obsidian blocks upward on each side.
Place two Obsidian blocks across the top to close the frame.
Leave the four corners empty or fill them with Obsidian; both versions work.
Hold Flint and Steel and use it on or inside the Obsidian frame.
Wait for the inside of the frame to turn purple, then step into the portal.
Use Creative mode materials
Creative mode is the easiest path when you do not want to mine Obsidian first. Enter Creative mode or create the world in Creative, then open the Creative Inventory.
Take Obsidian and Flint and Steel from the Creative Inventory. Build the same upright frame with a two-block bottom, two-block top, and three blocks on each side.
Use Flint and Steel on or inside the frame. The purple portal effect means it is active and ready to use.
Make a bigger decorative portal
Build a valid upright Obsidian frame larger than the smallest version.
Keep the usable frame made from regular Obsidian.
Use Flint and Steel or another fire-starting method on the completed frame.
Official Minecraft guidance confirms portal builds can be up to 23 blocks wide, so you have room to make a larger entrance.
Repair a ruined portal
This fixes broken portal structures you find in the Overworld or the Nether.
Find a Ruined Portal in the Overworld or the Nether.
Dig around the structure if part of it is buried.
Replace missing frame blocks with regular Obsidian.
Remove Crying Obsidian from the usable frame and replace it with regular Obsidian.
Light the completed frame with Flint and Steel or another fire-starting method.
Cast obsidian with lava and water
This method applies when you want a portal frame without mining Obsidian first. Minecraft guidance confirms that lava plus water can create Obsidian.
Place Lava source blocks where the frame’s Obsidian blocks should go.
Use Water so the Lava interacts with it and turns into Obsidian.
Repeat the process until the upright frame is complete.
Light the finished frame with Flint and Steel or a Fire Charge.
Fix a portal that will not light
The most common cause is an incomplete frame or the wrong block in the usable frame.
Check that the frame is upright and made from regular Obsidian.
Make sure the smallest frame has two Obsidian blocks on the bottom, two on the top, and three on each side.
Replace any Crying Obsidian in a repaired Ruined Portal, because the usable frame needs regular Obsidian.
Use Flint and Steel on or inside the completed frame again.
Light it with a Fire Charge
Craft a Fire Charge from Blaze Powder, Coal or Charcoal, and Gunpowder.
Hold the Fire Charge and use it on a surface in the completed frame.
For a dispenser setup, place the Fire Charge in a Dispenser facing the portal.
Activate the Dispenser so it fires the Fire Charge into the portal.
Use this method to relight a portal after it has gone out.
Use commands when allowed
On Bedrock, open Settings, then Game, then turn on the cheats toggle, labeled Allow Cheats or Activate Cheats depending on your version.
For an existing Java single-player world, open World Options and enable Allow Commands; those buttons are not available in Hardcore worlds. The Open to LAN route is a different control: Game Menu, then Open to LAN, then Settings for Other Players, then Allow Commands sets command access for players who join your world, not for you as the host. Open chat and run /give @s minecraft:obsidian 10 and /give @s minecraft:flint_and_steel 1, then build and light the portal normally.
You can also run /gamemode creative after commands are enabled, take Obsidian and Flint and Steel from the Creative Inventory, and build the portal from there. On Bedrock, enabling cheats disables achievements for that world.
On current Java servers where Nether portal travel was disabled, an operator or admin can run /gamerule allowEnteringNetherUsingPortals true. Current Java guidance replaced the old allow-nether=true server setting with this game rule.
If commands are unavailable, use the standard survival build or the Creative Inventory method allowed in your world.
Frequently Asked Questions
What is the smallest Nether portal you can make?
The smallest working frame has two obsidian blocks along the bottom, two along the top, and three obsidian blocks on each side. The corner blocks can be filled or left out.
Can Crying Obsidian be used in a Nether portal?
No. A usable Nether portal frame needs regular obsidian, so replace any Crying Obsidian in a ruined portal before lighting it.
How do you light a Nether portal without Flint and Steel?
Use a Fire Charge on the completed frame, or place a Fire Charge in a Dispenser facing the portal and activate the Dispenser.
Why did enabling commands affect my Bedrock world?
On Bedrock, turning on cheats disables achievements for that world. If you want achievements, use the normal survival method instead of commands.