X-Wing Technique in Sudoku: Multi-Line Elimination Guide

By Avi Israeli · Reviewed by Ninely Engine Logic Council · Updated November 2026

What is an X-Wing?

An X-Wing is a powerful multi-line candidate pattern that spans across two parallel rows and two intersecting columns (or vice versa).

When a specific candidate digit appears in exactly two cells in Row A, and in the exact same two columns in Row B:

  1. Because each row must contain that digit, one row will take the left column while the other row takes the right column (or vice versa).
  2. These two diagonal possibilities form an “X” shape.
  3. Either way, both columns are guaranteed to have their digit placed in one of those two rows.
  4. Therefore, that digit cannot appear anywhere else in those two columns!

Worked Example: X-Wing on Digit 4 Eliminates 4 from Cell R6C3

Observe digit 4 across Row 5 and Row 8 on the board below:

  • Row 5: Candidate 4 can only be placed in two columns: Column 3 (R5C3) and Column 7 (R5C7).
  • Row 8: Candidate 4 can also only be placed in the exact same two columns: Column 3 (R8C3) and Column 7 (R8C7).
  • The Rectangular Lock: If Row 5 places 4 at R5C3, then Row 8 must place 4 at R8C7. If Row 5 places 4 at R5C7, then Row 8 must place 4 at R8C3. In both outcomes, Column 3 and Column 7 have their 4s locked into Row 5 and Row 8!
  • Target Elimination at R6C3: Follow Column 3 down to cell Row 6, Column 3 (R6C3). This cell has candidates {2, 4}. Because the X-Wing claims Column 3's 4, candidate 4 is eliminated from R6C3, leaving 2 as a Naked Single!
X-Wing on 4: Rows 5 & 8 (Cols 3 & 7)
2 4 9
1 4
➔
Target Cell R6C3 (4 Eliminated)
2 4
5
8
9
6
1
7
9
8
5
3
4
6
4
3
1
7
5
9
8
2
1
6
4
7
5
8
3
249
14
6
5
7
24
9
3
2
5
3
3
1
45
2
9
48
7
6
8
7
2
Step 2 of 3: The 4 corners form an X-Wing lock across Col 3 and Col 7

⚠️ The Tempting Wrong Move: Placing 4 in R6C3

A player searching for a place to put 4 in Column 3 might guess 4 in R6C3 because the cell only has two candidates {2, 4}.

Why this fails: Placing 4 in R6C3 eliminates 4 from both R5C3 and R8C3 along Column 3. This forces Row 5 to place 4 at R5C7, and Row 8 to place 4 at R8C7. That puts two 4s directly in Column 7, causing an immediate, fatal contradiction!

💡 Solving Tip: The Fish Pattern Finder

X-Wing is the smallest member of the “Fish” family (where N parallel lines hold a candidate in the same N perpendicular lines). When you hit an advanced deadlock, pick one digit at a time and highlight all rows that have exactly two candidate cells for that digit. If two rows share the same two columns, you have found an X-Wing!

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