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Obsidian forms when water flows over a lava source block. To mine the finished block, use a diamond or netherite pickaxe. If you do not have either tool, you can cast obsidian directly in a temporary mold with lava and water, so a Nether portal is still possible early in a survival world.
A conventional portal frame is at least 4 blocks wide and 5 blocks tall. Leaving the four corners empty reduces the minimum to 10 obsidian; a complete 4×5 outline uses 14. Once the frame is built, ignite its empty 2×3 interior with flint and steel, a fire charge, or another suitable fire source.
What obsidian is and why it matters
Obsidian is a very durable building block created by the interaction of water and lava. The conversion works when water contacts a lava source block, not merely a stream of flowing lava. A source block is the still, full block that can be collected with a bucket. When water reaches it, the lava is replaced by obsidian.
That mechanic gives you two different ways to obtain portal material:
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- Mine it: convert lava sources with water, then break the obsidian with a diamond or netherite pickaxe.
- Cast it in place: arrange lava and water inside a temporary dirt or cobblestone mold, allowing the frame to harden where it will be used.
Obsidian is also found as generated loot or construction material. Ruined portals and certain structures in the Nether and End can supply additional blocks. Those sources are useful when you find them, but they are situational compared with a nearby lava pool.
How much obsidian a Nether portal needs
The smallest conventional portal has an outside size of 4×5 blocks: four blocks across and five blocks high. The four corner positions are optional, because the game checks the rectangular frame rather than requiring corner blocks. Omitting the corners gives a 10-block frame. Filling every position in the 4×5 outline gives 14 blocks.
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| Portal layout | Outside dimensions | Obsidian required | When to choose it |
|---|---|---|---|
| Cornerless minimum | 4×5 | 10 | Fastest and most material-efficient portal |
| Complete minimum outline | 4×5 | 14 | Easier to recognize and decorate |
| Larger rectangle | Up to 23×23 | Depends on the frame outline | Build space, entrances, or a decorative design |
For a cornerless 4×5 frame, the two vertical sides are three blocks tall between the bottom and top, and the top and bottom each contain two blocks between the sides. The interior opening is 2×3. Larger valid rectangles can be built through 23×23 blocks; the opening must remain clear and rectangular.
What you need before collecting obsidian
Prepare the site before touching a lava pool. At minimum, bring a bucket and a reliable water source. A second bucket makes moving water and lava easier, while dirt or cobblestone provides a safe temporary mold. Keep spare blocks for barriers and a safe route away from the pool.
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- For mining: a diamond or netherite pickaxe, a bucket of water, and blocks for safety.
- For casting: at least one bucket, a water source, lava sources, and dirt or cobblestone for the mold. You do not need a diamond pickaxe.
- For activation: flint and steel is the simplest option. A fire charge or another suitable fire source can also ignite the portal.
Work from the edge of a lava pool rather than standing on an exposed source. Place a water stream where it can spread across the area you intend to mine, and block unexpected lava flows before they reach your feet.
Method 1: Mine obsidian with a diamond or netherite pickaxe
This is the straightforward route when you already have the required pickaxe. It gives you portable blocks that can be used anywhere, but each block takes time to break and lava can remain underneath.
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- Locate a lava source. A surface lava pool is convenient, although any accessible group of source blocks works. Clear hostile mobs and make a retreat path before you begin.
- Secure water. Carry a filled bucket. Place water at the edge of the area so it flows across the lava you plan to convert. Water touching a lava source changes that source into obsidian.
- Expose one block at a time. Let water cover the working area, then inspect the obsidian surface for lava hidden below or beside it. Extend your safety platform with dirt or cobblestone before mining deeper.
- Mine with the correct pickaxe. Break each obsidian block using a diamond or netherite pickaxe. A weaker pickaxe may show a breaking animation but will not successfully collect the block.
- Control the water and lava. Replace water when you need to reveal another section, and plug newly exposed lava with blocks or water before stepping forward. Never assume the visible top is the whole pool.
- Count your haul. Gather at least 10 blocks for a cornerless portal or 14 for a fully outlined 4×5 frame. Collect extra pieces if you plan to relocate the portal, build a larger opening, or repair mistakes.
Mining is safest when the water remains between you and the unconverted lava. If a block breaks and lava appears underneath, move back, place water or a solid block, and only then continue.
Method 2: Cast a portal without a diamond pickaxe
Casting lets you create the frame in its final position. You place lava source blocks inside a temporary mold, flow water over them to turn them into obsidian, and repeat until the rectangle is complete. The method is slower to set up but avoids mining obsidian altogether.
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Build the temporary mold
- Choose a safe location. Use a flat area away from flammable structures. Leave room to stand beside every part of the future frame and to remove the mold afterward.
- Outline a 4×5 rectangle. Mark the bottom, sides, and top with dirt or cobblestone. Leave the four corners empty if you want the 10-block version. The mold should hold lava where each obsidian frame block will stand.
- Provide a working platform. Add temporary blocks behind or beside the vertical sides so you can place lava sources at the correct height without falling.
Place lava and convert it
- Place one lava source in a mold position. A source must occupy the exact location where you want the finished obsidian block. Flowing lava that does not become a source will not give you the intended frame block.
- Flow water over the source. Pour water so it contacts the lava. The source hardens into obsidian. Keep the water controlled so it does not wash you into another lava pocket.
- Move to the next position. Pick the water back up if necessary, place the next lava source, and repeat the conversion. Work from the bottom upward on the sides, then across the top.
- Remove temporary blocks. Once every required position has hardened, dismantle the dirt or cobblestone mold. Leave the obsidian frame and clear the 2×3 interior.
For a cornerless frame, cast 10 positions. If you prefer a complete outline, cast all 14 positions. Casting is forgiving because a misplaced block can be surrounded by temporary blocks and corrected before the portal is lit; however, breaking an unwanted obsidian block still requires a diamond or netherite pickaxe, so place each source carefully.
Construct the portal frame correctly
Build a vertical rectangle with an outside width and height between 4×5 and 23×23 blocks. The interior must be an unobstructed rectangle. A cornerless frame is valid, but the four side-to-top junctions still need to form a continuous shape that encloses the opening.
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|---|---|---|
| Bottom | Two obsidian blocks between the lower corners | Making the base only one block wide |
| Vertical sides | Three blocks high between the bottom and top | Stopping at two blocks, leaving an opening too short |
| Top | Two obsidian blocks between the upper corners | Building a horizontal line that is not connected to both sides |
| Interior | 2×3 clear opening | Leaving dirt, water, torches, or other blocks inside |
Corner blocks are optional for portal activation, not for visual symmetry. If you are following a building plan or want a conventional-looking rectangle, fill them. If resources are scarce, leave them out and spend the four saved blocks elsewhere.
How to light the Nether portal
- Clear the opening. Remove every temporary mold block and confirm that the interior is empty.
- Stand outside the frame. Face one of the interior blocks rather than stepping into the opening.
- Use flint and steel. Ignite a block inside the frame. The portal activates when the frame is valid and the interior catches fire.
- Use an alternative if needed. A fire charge or another suitable fire source can ignite the empty frame when flint and steel is unavailable.
Only the frame has to be obsidian; the fire that appears in the opening is the activation trigger. If nothing happens, extinguish stray fire, inspect the dimensions, and check that all required frame positions are present.
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Where to get more obsidian
Ruined portals
Ruined portals are pre-generated structures that contain obsidian or partly built frames. Salvaging their blocks can save mining time, although the structure may be incomplete and may include damaged or obstructed sections. Bring a suitable pickaxe if you intend to collect the blocks rather than use the existing frame.
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Certain structures in the Nether and End contain obsidian as part of their construction or generated resources. These locations are exploration options rather than dependable first-portals: reaching them requires an existing route and can expose you to more dangerous environments.
Advanced renewable sources
Experienced players can use advanced portal-based or End-based techniques to produce obsidian repeatedly. These methods depend on the current game edition and release, careful construction, and a safe operating area. Treat them as infrastructure projects, not as a replacement for the simple lava-and-water method in a new world.
Safety practices around lava and portals
- Make an escape route first. A two-block-high tunnel or a solid platform gives you somewhere to retreat if lava spreads or a hostile mob appears.
- Use nonflammable scaffolding. Cobblestone and similar blocks are safer than wood around open lava and portal fire.
- Do not mine blindly. Obsidian can cover additional lava. Keep water available and expose one block at a time.
- Secure the portal room. Roofs, walls, lighting, and a door reduce the chance of mobs entering while you are returning from the Nether.
- Carry spare blocks. They can plug lava, bridge gaps, mark your route, or close an unsafe portal approach.
Troubleshooting a portal that will not activate
The opening is too small
Measure the outside rectangle. The minimum is 4 blocks wide by 5 blocks tall. A frame that is only 3 blocks wide or 4 blocks tall cannot create the required 2×3 interior.
A frame position is missing
Check both vertical sides, the bottom, and the top. Cornerless construction is allowed, but removing any non-corner position breaks the enclosure.
The interior is blocked
Remove mold blocks, water, decorative blocks, and any other obstruction from the opening. Light the fire on an interior block after the space is clear.
The fire source is not suitable
Try flint and steel first. If you are using a fire charge or another method, make sure the fire actually appears inside the frame rather than beside it.
You are troubleshooting portal linking
Travel between portals can behave differently across Java and Bedrock and can change with game releases. Confirm the current edition and version before relying on exact linking distances or coordinates. The frame itself still needs to be valid and lit before linking can be evaluated.
Quick Recap
Choosing the best method
| Your situation | Best approach | Trade-off |
|---|---|---|
| You have a diamond or netherite pickaxe and a nearby lava pool | Convert and mine the pool | Portable blocks, but mining is time-consuming and exposes hidden lava |
| You have no qualifying pickaxe | Cast the frame in a dirt or cobblestone mold | Uses careful placement and repeated water handling, but works early in survival |
| You find a ruined portal | Salvage or complete the existing structure | Fast when nearby, but the structure may be incomplete or inconveniently located |
| You are building a long-term base network | Plan a larger frame or advanced renewable supply | More construction and version-specific planning than a first portal requires |
Practical checklist
- Locate a safe lava source and secure water.
- Choose mining if you have a diamond or netherite pickaxe; otherwise prepare a dirt or cobblestone mold.
- Collect or cast 10 obsidian for a cornerless 4×5 frame, or 14 for a complete outline.
- Keep the frame within the valid 4×5 to 23×23 outside dimensions.
- Clear the 2×3 minimum interior and remove every temporary block.
- Ignite the opening with flint and steel, a fire charge, or another suitable fire source.
- Build barriers, an escape route, and a protected portal room before making repeated trips.
- For unusual portal-linking behavior, check the current Java or Bedrock release rather than assuming rules from another edition.
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