Volodymyr Sakhan  ·  April 17, 2026

Hidden Pairs is one of the most rewarding intermediate sudoku techniques. When two candidates appear in exactly two cells of a house (row, column, or box) — and nowhere else in that house — those two digits must go into those two cells. Any other candidates those cells carry can be safely eliminated.

The pair is "hidden" because the two cells often hold several other candidates that obscure the pattern. Once you spot it, you strip the cells down to just the pair — sometimes turning a complex position into a cascade of easy moves. You'll need full pencil marks to apply this technique reliably.

What Is a Hidden Pair?

A Hidden Pair exists when exactly two cells in a house share two candidates that do not appear in any other cell of that house. Because those two digits have nowhere else to go, one cell must hold one digit and the other cell must hold the other — the assignment is forced, even if you don't yet know which way around.

The consequence is powerful: every other candidate in those two cells is impossible. You can eliminate them all immediately. Compare this with a Naked Pair, where both cells already contain only the two shared candidates. In a Hidden Pair the extra candidates are still present — that is what makes the pair "hidden" and what you are eliminating.

When to Use Hidden Pairs

Hidden Pairs are an intermediate technique — apply them after you have exhausted easier methods. Look for them when:

• You have complete pencil marks in every empty cell and no basic singles (Last Free Cell, Last Remaining Cell, Last Possible Number) remain.
• A scan for Naked Pairs has turned up nothing, or further eliminations are still needed to unlock the puzzle.
• You notice a candidate that appears in only two cells of a row, column, or box — check immediately whether a second candidate shares the same two cells.

Step-by-Step Example

Let's walk through two concrete examples — one Hidden Pair in a row and one in a box — to show exactly how the pattern is found and applied.

Hidden Pair in a Row

In row 3, cells D3, F3, and G3 are already filled (6, 2, and 9). The six remaining empty cells are A3, B3, C3, E3, H3, and I3. After filling in pencil marks, candidates 4 and 8 appear only in A3 and I3 — the four middle cells (B3, C3, E3, H3) cannot hold 4 or 8 because their columns already contain those digits. A3 shows {1, 3, 4, 8} and I3 shows {4, 5, 7, 8}.

1. Write complete pencil marks for all empty cells in row 3.
2. Scan each candidate to count how many cells it appears in. When you find one that appears in exactly two cells, check whether any other candidate is also confined to those same two cells.
3. Notice that 4 appears only in A3 and I3. Confirm: check B3, C3, E3, H3 — none can hold 4 because columns B, C, E, and H each already contain a 4.
4. Check 8 the same way: it also appears only in A3 and I3 in this row, for the same reason (columns B, C, E, and H each contain an 8).
5. Since both 4 and 8 are confined to A3 and I3, those two cells form a Hidden Pair {4, 8}. One cell will be 4 and the other will be 8.
6. Eliminate all other candidates from A3: remove 1 and 3. A3 is now {4, 8}.
7. Eliminate all other candidates from I3: remove 5 and 7. I3 is now {4, 8}. A3 and I3 are now a Naked Pair — further eliminations in row 3 and their respective boxes may follow.

When two candidates appear in exactly two cells of a row, those cells form a Hidden Pair — every other candidate in those two cells can be eliminated.

Hidden Pair in a Box

In box 9 (bottom-right box, rows 7–9, columns G–I), cell G7 is filled (7) and I8 and H9 are filled (8 and 3). Of the four remaining empty cells, I7 and I9 cannot hold 2 or 4 because column I already contains both digits (2 at row 2, 4 at row 4). G8 and H8 cannot hold them because row 8 already contains both (4 at column A, 2 at column D). That leaves H7 and G9 as the only cells in the box that can hold 2 or 4. H7 shows {1, 2, 4, 6, 9} and G9 shows {1, 2, 4, 5, 9}.

1. Fill in pencil marks for all empty cells in box 9.
2. Notice that candidates 2 and 4 are absent from I7 and I9 — column I already contains both digits (2 at row 2, 4 at row 4), so no cell in column I can hold them.
3. Notice the same for G8 and H8 — row 8 already contains both 2 (at column D) and 4 (at column A), eliminating them from every empty cell in row 8.
4. That leaves only H7 and G9 as possible homes for 2 and 4 within box 9. Since both digits must appear exactly once in the box, H7 and G9 form a Hidden Pair {2, 4}.
5. Eliminate all non-{2, 4} candidates from H7: remove 1, 6, and 9. H7 is now {2, 4}.
6. Eliminate all non-{2, 4} candidates from G9: remove 1, 5, and 9. G9 is now {2, 4}.

A Hidden Pair in a box is found exactly the same way as in a row or column — scan for two candidates that have no other home in the box, then strip everything else from those two cells.

Hidden Pairs vs. Naked Pairs

Both techniques reserve two cells for two specific digits, but the perspective is different:

• Naked Pair: two cells each contain only the two shared candidates. The pair is immediately visible from the cell contents. You eliminate those two digits from every other cell in the house.
• Hidden Pair: the two cells also hold extra candidates — the pair is revealed only by scanning where each candidate can go across the whole house. You eliminate every other candidate from those two cells.
• Tip: if a Naked Pair scan turns up nothing, switch perspective. Instead of looking at what's in each cell, look at where each candidate can go. When a digit fits in only two cells, note it — then check whether a second digit shares the same two homes.
• Hidden Pairs work identically in rows, columns, and boxes — the house type does not change the logic.

After mastering Hidden Pairs you are ready for Hidden Triples — the same idea extended to three candidates confined to three cells.

Practice Hidden Pairs Online

Hidden Pairs appear regularly on hard and expert sudoku puzzles. Open pencil marks on a hard sudoku, complete your candidate notes for every empty cell, then scan each house for any digit that sits in exactly two cells. If you find a second digit sharing the same two cells, you have a Hidden Pair — eliminate everything else from those two cells and watch the position open up.

For more techniques at every level, visit our complete sudoku solving guide.