Claiming Sudoku: How Line-to-Box Elimination Removes Candidates

Claiming Sudoku is one of the most useful locked-candidate techniques for solvers who are ready to move beyond singles but do not want to guess. If all possible places for one digit in a row or column fall inside the same 3×3 box, that digit can be removed from the other cells in that box.

This matters because many puzzles stall in the middle. You can see candidates, but no cell looks ready to place. Claiming helps you turn line information into box eliminations, which often opens the grid again without needing a harder pattern.

Quick Answer: What Is Claiming in Sudoku?

Claiming in Sudoku happens when all remaining candidates for one digit in a row or column are confined to a single 3×3 box. Because that digit must appear in that line inside the box, the same digit can be eliminated from the other unsolved cells in that box.

Featured snippet answer: Claiming in Sudoku is a locked-candidate technique where a row or column forces a digit to stay inside one 3×3 box. That lets you remove the same digit from the other cells in the box outside that row or column.

How Claiming Sudoku Works

The logic is simpler than the name sounds:

  1. Choose one digit, such as 8.
  2. Look across one row or one column.
  3. If every possible 8 in that line lies inside the same 3×3 box, then the line has already claimed the 8 inside that box.
  4. Because the digit must stay in those line cells, no other cell in that box can contain 8.

You are not placing the digit immediately. You are removing impossible candidates from the rest of the box so the next scan becomes easier.

Claiming Pair vs Claiming Triple

Players sometimes search for claiming pair Sudoku and claiming triple Sudoku as if they are different techniques. They are the same elimination rule.

  • Claiming pair: the digit has two candidate cells in a row or column, and both are inside the same box.
  • Claiming triple: the digit has three candidate cells in a row or column, and all three are inside the same box.

The number of line candidates changes, but the logic does not. If the line restricts the digit to one box, the rest of that box loses the digit.

Claiming Sudoku Example

Imagine row 6 still needs a 4. After checking column restrictions, the only places left for 4 on that row are two cells, and both of them sit inside the middle-right 3×3 box.

That means row 6 has already claimed the 4 inside that box. Even if you do not yet know which of those two cells is correct, every other 4 candidate elsewhere in that box is wrong and can be erased.

That single cleanup step often creates one of three useful outcomes:

  • a hidden single inside the box,
  • a cleaner pair in a crossing row or column, or
  • a new follow-up elimination such as pointing or a subset.

Why Claiming Matters in Real Puzzles

Claiming is valuable because it teaches you to read the grid in both directions. Beginners usually scan rows, columns, and boxes as separate units. Claiming shows that a row can control a box, just as pointing pairs in Sudoku show that a box can control a line.

It is especially useful when:

  • hidden singles have stopped appearing,
  • your notes are accurate but crowded,
  • the puzzle feels close to reopening, and
  • you want progress without escalating to fish or chain logic.

Where Claiming Fits in Your Solve Order

For most improving solvers, claiming belongs in the same layer as other locked-candidate techniques. It should usually come after singles and basic note cleanup, but before heavier intermediate or advanced patterns.

  1. Scan for naked singles.
  2. Scan for hidden singles.
  3. Clean obvious notes.
  4. Check boxes for pointing patterns.
  5. Check rows and columns for claiming patterns.
  6. Then move to subsets, candidate lines, or harder eliminations.

If you want the broader progression, Pure Sudoku’s guide on what to try after hidden singles in Sudoku is the best next read.

How to Spot Claiming Sudoku Faster

The fastest way to find claiming Sudoku patterns is to stop scanning randomly and use one repeatable loop:

  1. Pick one digit.
  2. Check a row.
  3. Ask whether every remaining candidate for that digit in the row sits inside one box.
  4. If yes, remove that digit from the other cells in the box.
  5. Repeat the same scan for columns.

This works best when your pencil marks are clean. If the grid still feels noisy, review how to read a candidate grid in Sudoku before hunting for locked candidates.

Claiming vs Pointing in Sudoku

Claiming and pointing belong to the same family, but the direction is reversed.

  • Claiming: the line restricts the box.
  • Pointing: the box restricts the line.

If you confuse them, remember this shortcut: claiming starts from a row or column scan, while pointing starts from a box scan. Both are forms of intersection removal Sudoku.

Common Claiming Mistakes

Eliminating from the row instead of the box

Claiming removes candidates from the rest of the box, not from the row or column you started with. The line cells are the reason the move works, so they stay.

Missing another line candidate outside the box

If the same digit still appears elsewhere in that row or column outside the box, the pattern is not a valid claiming move. Verify the full line before you eliminate anything.

Not checking both rows and columns

Many players only notice claiming horizontally. The exact same logic works vertically when a column locks one digit into a single box.

Jumping to advanced methods too soon

Claiming is one of the best midgame cleanup tools because it is simple, fast, and reliable. Do not skip it when the puzzle feels stuck after singles.

FAQ

What is claiming in Sudoku?

Claiming is a locked-candidate technique where all candidates for one digit in a row or column are confined to one 3×3 box, allowing eliminations from the rest of that box.

Is claiming the same as locked candidates type 2?

Yes. Many guides call claiming locked candidates type 2. The logic is the same even if the name changes.

Does claiming place a number directly?

Usually no. Claiming is mainly an elimination tool. Its value comes from the singles or cleaner patterns it unlocks immediately afterward.

Is claiming harder than pointing pairs?

Not really. They are sister techniques. Some players find pointing easier first because the box pattern is more visual, but the logic level is similar.

When should I look for claiming in Sudoku?

Look for claiming after singles and note cleanup, especially when a row or column has only a few remaining positions for one digit.

Conclusion

Claiming Sudoku is one of the cleanest ways to restart a stalled puzzle without guessing. Once you see that a row or column has forced a digit into one box, the rest of that box becomes easier to untangle.

On your next puzzle, scan line by line and ask one simple question: are all remaining spots for this digit inside the same box? If they are, claim the box and clear the noise. For more locked-candidate practice, continue with pointing pairs in Sudoku and related guides at Pure Sudoku.