Hidden Pairs in Sudoku: How to Find Them Step by Step
By Michel ·
You have filled in the obvious singles. Your pencil marks are neat. You have scanned every row, column, and box, and nothing new jumps out. Sound familiar?
When singles stop giving you a move, hidden pairs and triples are useful patterns to check. They will not resolve every stuck grid, but they can remove candidates without choosing a value by guesswork. Start with accurate notes and look at where each digit can still go.
What Is a Hidden Pair?
A hidden pair occurs when two candidates appear in exactly two cells within a single unit (a row, column, or box), and those two candidates are not found anywhere else in that unit.
The word "hidden" is key. Unlike a naked pair, where two cells contain only the same two candidates and nothing else, a hidden pair is buried among other candidates in those cells. The extra pencil marks act as camouflage, making the pair easy to overlook.
Worked example: Imagine a 3×3 box where five cells still have candidates. You notice that digits 3 and 7 only appear in two of those cells. Cell A has candidates {1, 3, 5, 7} and Cell B has candidates {3, 6, 7}. Because 3 and 7 cannot go anywhere else in this box, they must occupy Cells A and B. Remove all other candidates from those two cells — Cell A becomes {3, 7}, Cell B becomes {3, 7}. These eliminations leave both cells with {3, 7}; they do not yet tell you which cell contains which digit.
| 8 | 1, 3, 5, 7 | 3, 6, 7 |
| 2 | 5, 6 | 5, 6 |
| 4 | 1, 5 | 9 |
How to Find Hidden Pairs: Step by Step
- Pick a unit. Start with a row, column, or box.
- Count candidate appearances. For each missing digit in that unit, note which cells contain it as a candidate.
- Look for digits that appear in exactly two cells. If two different digits share the same two cells, and only those two cells, you have a hidden pair.
- Eliminate the extras. Remove every other candidate from those two cells. The pair is locked in.
Practical tip: focus on the digits, not the cells. Ask "Where can 4 go in this row?" instead of "What can go in this cell?" That shift makes hidden pairs far easier to spot.
Hidden Triples: The Same Logic, One More Cell
A hidden triple works just like a hidden pair, but with three candidates spread across exactly three cells in a unit. The tricky part: not every candidate needs to appear in all three cells.
Example — digits 2, 5, and 8 distributed in a column:
- Cell X: {2, 5, 6, 9} → becomes {2, 5}
- Cell Y: {1, 2, 8} → becomes {2, 8}
- Cell Z: {4, 5, 8} → becomes {5, 8}
If 2, 5, and 8 appear only in these three cells within that column, remove all other candidates from them. The rule only requires that the three candidates collectively occupy exactly three cells.
When to Look for Hidden Pairs and Triples
Use this solving order:
- Naked and hidden singles first — always exhaust these before anything else.
- Locked candidates — check for pointing pairs and box/line reduction.
- Hidden pairs and triples — when the grid feels stuck after the steps above.
Difficulty labels do not guarantee a hidden pair. Use them to choose a comfortable puzzle, then let its candidates guide you:
- Easy / Medium: Start with singles and scan each unit before looking for pairs.
- Hard: Check candidate locations when basic scanning stops producing moves.
- Expert: Pairs or triples may help, but the next deduction depends on the grid.
- Master: A harder label does not tell you which technique to apply first.
Hidden Pairs vs. Naked Pairs: What Is the Difference?
Players often confuse these two. The key difference is where you eliminate candidates:
| Naked Pair | Hidden Pair | |
|---|---|---|
| Cell contents | Exactly 2 candidates, same two digits | Multiple candidates — pair is hidden among them |
| Eliminate from | Other cells in the unit | Within the two cells themselves |
| How to spot | Look at cells: which have only 2 candidates? | Look at digits: which appear in only 2 cells? |
Common Mistakes
- Confusing hidden pairs with naked pairs. With naked pairs you eliminate from surrounding cells; with hidden pairs you eliminate from the pair cells themselves.
- Eliminating too broadly. Only remove extra candidates from the pair/triple cells — not from other cells in the unit.
- Forgetting overlapping units. After a hidden pair elimination, check whether new singles appear in the overlapping row/column/box.
Practice
The best way to internalize hidden pairs and triples is repetition. Try an expert sudoku puzzle on Sudoku a Day. For an even bigger challenge, explore master difficulty puzzles. Neither label guarantees a hidden pair or triple. It can also help to check pointing pairs before searching for more complex patterns. For a wider selection of techniques, check our sudoku strategies guide for a full progression from beginner to advanced.
Frequently Asked Questions
What is a hidden pair in sudoku?
A hidden pair is two candidates that appear in exactly two cells within a row, column, or box, and nowhere else in that unit. Other candidates may also be present in those two cells. Once identified, you can remove all other candidates from those two cells.
How do hidden pairs differ from naked pairs?
In a naked pair, two cells contain only the same two candidates. In a hidden pair, those two cells also contain other candidates. With naked pairs you eliminate from surrounding cells; with hidden pairs you eliminate the extra digits from the pair cells themselves.
How do I spot a hidden triple?
Look for three candidates that collectively appear in only three cells within a unit. Not all three candidates need to appear in every cell. If those three digits cannot be found anywhere else in the unit, you have a hidden triple.
When should I use hidden pairs vs other advanced techniques?
Try hidden pairs when singles and locked candidates no longer offer progress. Apply them only when two digits share exactly the same two possible cells in one unit; an expert or master label alone is not evidence of that pattern.