Pick a unit and ask which cells each digit can still go in. When two digits are restricted to the same two cells, those cells belong to that pair alone, so strip out every other candidate from them. The result is a Naked Pair that often unlocks further eliminations.
What Is It?
A Hidden Pair occurs when two digits appear as candidates in exactly the same two cells within a unit, and nowhere else in that unit. Since both digits must go in those two cells, all other candidates in those cells can be removed.
The pair is "hidden" because the two cells typically contain additional candidates that obscure the pattern. A cell might show {1, 3, 5, 8} while its partner shows {3, 5, 7, 9}. The digits 3 and 5 only appear in these two cells within the unit. That's your Hidden Pair. Remove everything except 3 and 5 from both cells.
Hidden Pairs are harder to spot than Naked Pairs because you're looking for what's exclusive to two cells rather than what's common between two minimal cells. They appear in Medium and Hard puzzles, often alongside Locked Candidates.
How It Works
Instead of looking at cells (like you do for Naked Pairs), look at digits. Pick a unit, say box 5, and ask: "For each digit, which cells can contain it?" If two digits share exactly the same two cells and appear nowhere else in that unit, you've found a Hidden Pair.
Suppose in box 5, digit 2 can only go in R4C5 or R6C4, and digit 8 can also only go in R4C5 or R6C4. No other cell in box 5 has 2 or 8 as a candidate. Since both 2 and 8 must go in these two cells, remove all other candidates from R4C5 and R6C4. They become {2, 8} each, which is now a Naked Pair.
This is the key insight: a Hidden Pair becomes a Naked Pair after you clean up the extra candidates. The elimination doesn't directly place digits, but it simplifies the cells dramatically, often triggering further techniques.
You can find Hidden Pairs in rows, columns, or boxes. Check each digit's candidate positions within a unit. If two digits always share the same two positions, that's your pair.
Worked Examples
Example 1: Hidden Pair in a Row
Examine row 6 and map where each unplaced digit can go. Digit 6 can only appear in R6C1 and R6C7. Digit 8 can also only appear in R6C1 and R6C7. No other cell in row 6 has 6 or 8 as a candidate.
In row 6, digits 6 and 8 can only appear in R6C1 and R6C7 (green). No other cell in the row has 6 or 8. This is a Hidden Pair.
Since digits 6 and 8 must occupy R6C1 and R6C7, all other candidates in those cells can be removed. R6C1 has {4, 6, 8}, remove 4, leaving {6, 8}. R6C7 has {6, 7, 8, 9}, remove 7 and 9, leaving {6, 8}.
Green circles: the Hidden Pair digits (6 and 8) locked to these two cells. Red circles: extra candidates (4, 7, 9) that must be removed from the pair cells.
Both cells now show {6, 8}, a clean Naked Pair. The Hidden Pair has simplified two busy cells, potentially unblocking further techniques in the intersecting columns and boxes.
Extra candidates eliminated from R6C1 and R6C7 (red strikethrough). The pair cells now contain only {6, 8}.
Example 2: Hidden Pair in a Box
Now look at box 7 (bottom-left). Map digit positions: digit 2 can only go in R7C3 and R8C1. Digit 8 can also only go in R7C3 and R8C1. No other cell in box 7 has 2 or 8.
In box 7, digits 2 and 8 can only appear in R7C3 and R8C1 (green). No other cell in the box has 2 or 8. This is a Hidden Pair.
Since 2 and 8 are confined to these two cells, remove all other candidates. R7C3 has {2, 4, 6, 7, 8}, remove 4, 6, and 7, leaving {2, 8}. R8C1 has {2, 7, 8}, remove 7, leaving {2, 8}.
Green circles: the Hidden Pair digits (2 and 8) locked to these two cells. Red circles: extra candidates (4, 6, 7) that must be removed from the pair cells.
The pair cells are now simplified to {2, 8}. Notice how the pair was "hidden" among many other candidates, you wouldn't have spotted it by looking at the cells alone.
Extra candidates eliminated from R7C3 and R8C1 (red strikethrough). The pair cells now contain only {2, 8}.
Example 3: Hidden Pair in a Column
In column 4, digits {1, 4} only appear in cells R5C4 and R8C4.
In column 4, digits 1 and 4 can only go in two cells: R5C4 and R8C4. No other cell in column 4 has either 1 or 4 as a candidate. Since both digits must go in these two cells, remove all other candidates: remove 9 from R5C4 (was {1, 4, 9}) and remove 7 from R8C4 (was {1, 4, 7}).
{1, 4} are hidden in R5C4 and R8C4. Remove other candidates from these cells.
Eliminated {7, 9} from R5C4, R8C4.
Hidden Pairs require looking at digits, not cells. For each unplaced digit in a unit, ask: "How many cells can hold this digit?" When two digits share exactly two cells, you've found a Hidden Pair.
Frequently Asked Questions
How do I spot a Hidden Pair?
Look at digits rather than cells. Take one unit and, for each unplaced digit, list the cells that can still hold it. If two digits map to exactly the same two cells and appear nowhere else in that unit, you have a Hidden Pair. Pencil marks make this scan far easier.
Can the two cells contain other candidates as well?
Yes, and that is exactly what makes the pair hidden. One cell might read {1, 3, 5, 8} and its partner {3, 5, 7, 9}. If 3 and 5 appear in no other cell of the unit, they are a Hidden Pair, and the 1, 8, 7 and 9 all come out.
What is the difference between a Naked Pair and a Hidden Pair?
A Naked Pair is two cells that hold the same two candidates and nothing else, so you remove those two digits from the rest of the unit. A Hidden Pair is two digits confined to two cells that may hold extra candidates, so you remove the extras from the pair’s cells instead.
What if one of the two digits also appears in a third cell?
Then it is not a Hidden Pair and the elimination is invalid. Both digits must be confined to the same two cells within the unit. If digit 3 can also go in a third cell, 3 might land there instead, and stripping candidates from your two cells would remove a digit the solution needs.
Does a Hidden Pair let me place a digit straight away?
No. A Hidden Pair never places a digit on its own; it only clears the extra candidates out of the two cells. What you gain is simplification: the two cells become a clean Naked Pair, which frequently exposes Naked Singles or Locked Candidates elsewhere. Re-scan the affected row, column and box afterwards.
Where are Hidden Pairs easiest to find?
Rows and columns, where the cells lie in a straight line and the digit-by-digit scan is easy to follow. Hidden Pairs also occur in boxes, where the logic is identical but the three-by-three layout makes them spatially harder to see. They turn up in Medium and Hard puzzles, often alongside Locked Candidates.
Key Points to Remember
- Look at digits, not cells. A Hidden Pair is about two digits that share exactly two cells within a unit.
- The two digits must appear in those two cells only. If either digit also appears in a third cell in the unit, it's not a Hidden Pair.
- The action is the opposite of Naked Pair: instead of eliminating the pair's digits from other cells, you eliminate other digits from the pair's cells.
- Hidden Pairs are most commonly found in rows and columns. In boxes, they're the same logic but spatially harder to see.
- After cleaning up a Hidden Pair, you often reveal Naked Pairs or Locked Candidates. Always re-scan the affected cells.
The best way to master Hidden Pair is to practice spotting it in real puzzles.