X-Wing Sudoku Technique

Updated 11 August 2026

An X-Wing is a fish pattern where a digit is confined to the same two lines — the same two columns across two rows, or the same two rows across two columns — which lets that digit be erased from every other cell along those two lines.

When an X-Wing applies

Subsets reason inside a single unit. Fish patterns are the first techniques on this list that reason across two units of the same kind at once — two rows, or two columns. An X-Wing needs a digit that, in two separate rows, can only go in exactly two cells each. If those four cells line up in exactly two columns, the digit is trapped in a rectangle: whichever row eventually takes it in one column, the other row must take it in the other column. Either way, no cell outside those two rows can hold the digit in either of those two columns, so every other candidate for it in those columns is impossible.

The same logic runs sideways: two columns with exactly two candidate cells each, aligned on the same two rows, trap the digit just as tightly and let it be erased from the rest of those two rows instead. X-Wings are the smallest fish, sized at two lines by two lines; Swordfish and Jellyfish, later on this list, stretch the same idea to three and four lines.

Worked example

Look at rows 5 and 6. In row 5, the only cells that can still hold 2 are r5c1 and r5c4. In row 6, the only cells that can still hold 2 are r6c1 and r6c4. Both rows restrict the digit to exactly the same pair of columns, 1 and 4, so the four corner cells r5c1, r5c4, r6c1 and r6c4 form an X-Wing on 2.

One of those two rows must place 2 in column 1, and the other must place it in column 4 — there is no third option, because nowhere else in either row can 2 go. That means column 1 and column 4 each get their 2 from row 5 or row 6, which is enough to rule the digit out everywhere else in both columns. r7c4 carried 2, 5, 6 and 9 before the deduction; the X-Wing removes the 2 and leaves 5, 6 and 9 behind. No other cell in columns 1 or 4 outside rows 5 and 6 still had 2 as a candidate on this board, so r7c4 is the pattern’s only elimination here.

How to spot an X-Wing

1. Pick a digit and scan the rowsFor one digit at a time, note every row where it has exactly two remaining candidate cells. Rows with three or more candidates for that digit are not useful here.
2. Compare the columns those cells sit inTake any two such rows and check whether their candidate cells share the same two columns. If they do, the four cells form a rectangle.
3. Confirm the rectangle is exactBoth rows must be limited to precisely those two columns for the digit. A stray third candidate cell in either row breaks the pattern completely.
4. Erase the digit from the rest of both columnsRemove the digit from every other cell in the two columns, outside the two base rows, then repeat the search on the column axis.

Common mistakes

• Eliminating the digit from cells inside the two base rows. The rows are exactly where the digit is still allowed; the eliminations only apply to the two columns outside them.
• Accepting a row with three candidate cells for the digit as one corner of the rectangle. A basic X-Wing needs precisely two candidate cells in each base row.
• Mixing up rows and columns mid-search. A row-based X-Wing eliminates along columns; a column-based X-Wing eliminates along rows. Keep the base and cover lines straight.
• Giving up because the grid looks crowded. X-Wings hide in wide candidate lists just as easily as in narrow ones — what matters is the digit’s own count per row or column, not how full the cells look.