Sudoku Candidate Strategy
Hidden Pair Sudoku Technique: Step-by-Step Guide
Learn how to find Hidden Pairs in rows, columns, and 3×3 boxes, remove extra candidates correctly, and uncover important number relationships inside crowded candidate lists.
Two Numbers Hidden in Two Cells
A Hidden Pair appears when two candidates can go nowhere else in a unit, even though the two cells contain additional notes.
Track Candidate Positions
Hidden Pairs are found by checking where numbers can appear, not by matching identical cells.
Find Two Restricted Numbers
Look for two candidates that appear only in the same two cells of one unit.
Remove Other Notes
Keep the two hidden candidates and remove unrelated candidates from the pair cells.
What Is a Hidden Pair in Sudoku?
A Hidden Pair occurs when two candidates can appear only in the same two cells inside one row, column, or 3×3 box.
Those two cells may contain additional candidates, which makes the pair difficult to notice. Once you prove that the two important candidates cannot appear anywhere else in the unit, every other candidate can be removed from those two cells.
For example, if candidates 2 and 8 appear only in two cells of a row, those cells must contain 2 and 8 in some order. Any extra candidates written in those cells are impossible.
Why Is It Called a Hidden Pair?
It is called “hidden” because the important pair is mixed with extra candidates. The two cells do not initially look like a matching pair.
Simple Example
Cell A = {2,4,8}
Cell B = {2,6,8}
If candidates 2 and 8 appear nowhere else in the unit, remove 4 from Cell A and 6 from Cell B. Both cells become {2,8}.
How to Find a Hidden Pair
Choose One Unit
Study one row, column, or 3×3 box at a time.
Check Each Missing Number
Count where every missing candidate can appear in the selected unit.
Find Two Candidates Sharing Two Cells
Look for two candidates that both appear only in the same two cells.
Remove Other Candidates From the Pair Cells
Keep the two hidden candidates and delete unrelated notes from those two cells.
Rescan the Puzzle
The reduced candidate lists may reveal singles, naked pairs, or another useful pattern.
Hidden Pair in a Row
Suppose candidates 3 and 9 appear only in R4C2 and R4C7 within row 4.
Row Example
If 3 and 9 appear nowhere else in row 4, remove 1 and 6 from R4C2 and remove 2 and 8 from R4C7. Both cells become {3,9}.
Hidden Pair in a Column
A column-based Hidden Pair works the same way. Two candidates must be restricted to the same two cells in one column.
Column Example
If candidates 4 and 7 appear only in R2C6 and R8C6 within column 6, remove all other candidates from those two cells.
The cells do not need to be next to each other. They only need to belong to the same column.
Hidden Pair in a 3×3 Box
Hidden Pairs can also appear inside a 3×3 box. Check candidate positions for every missing number in the box.
Box Example
If candidates 1 and 5 can appear only in two cells of the centre box, remove every other candidate from those two cells.
A Hidden Pair in a box may also interact with a row or column, but eliminations outside the two cells require a separate valid technique.
Why the Hidden Pair Elimination Is Valid
Every missing number must appear once in each row, column, and box. If candidates 2 and 6 can appear only in the same two cells of a unit, those cells must contain 2 and 6 in some order.
Possibility A
First cell = 2
Second cell = 6
Possibility B
First cell = 6
Second cell = 2
Either way, every other candidate in those two cells is impossible and can be removed.
When Should You Look for a Hidden Pair?
When Candidate Lists Are Crowded
Hidden Pairs are useful when many cells contain three or more candidates.
After Singles and Naked Pairs Stop
Check easier techniques first, then inspect candidate positions for hidden restrictions.
In Hard and Expert Sudoku
Hidden Pairs commonly appear in harder puzzles where candidate lists are more complex.
When Two Numbers Have Very Few Positions
A unit where several numbers appear only twice is a strong place to search.
When Is It Not a Hidden Pair?
❌ One Candidate Appears Elsewhere
If either candidate can appear in a third cell of the unit, the pair is not locked.
❌ The Candidates Use Different Cells
Both candidates must be restricted to exactly the same two cells.
❌ The Cells Do Not Share a Unit
Two cells cannot form a Hidden Pair unless they share one row, column, or box.
❌ Candidate Notes Are Incomplete
Missing notes can make two candidates appear more restricted than they really are.
Common Hidden Pair Mistakes
❌ Looking Only at Bivalue Cells
Hidden Pairs often appear in cells with three or four candidates, so do not search only for two-candidate cells.
❌ Removing the Pair Candidates
Keep the two hidden candidates. Remove only unrelated candidates from the pair cells.
❌ Eliminating From Other Cells
A Hidden Pair eliminates extra notes inside the pair cells, not candidates from other cells in the unit.
❌ Confusing It With a Naked Pair
A Naked Pair starts with two matching bivalue cells. A Hidden Pair starts with two restricted candidate numbers.
Hidden Pair vs. Naked Pair
For more examples, read our Naked Pair Sudoku guide.
Hidden Pair vs. Hidden Triple
Hidden Pair Practice Checklist
- 1. Are the two candidates inside the same row, column, or box?
- 2. Does each candidate appear only in the same two cells?
- 3. Have you confirmed that neither candidate appears in a third cell?
- 4. Are the candidate notes complete and current?
- 5. Are you keeping the hidden pair candidates?
- 6. Are you removing only unrelated candidates from the pair cells?
- 7. Did you rescan after simplifying the pair?
Related Sudoku Learning Pages
🧠 Advanced Sudoku Techniques
Learn subsets, X-Wing, Swordfish, wings, coloring, unique rectangles, and chains.
👯 Naked Pair Sudoku
Learn how two matching bivalue cells eliminate candidates from the rest of a unit.
✖️ X-Wing Sudoku
Learn the four-corner candidate pattern used across two rows and two columns.
🟠 Hard Sudoku
Practise candidate-position analysis and Hidden Pair recognition.
Frequently Asked Questions
What is a Hidden Pair in Sudoku?
A Hidden Pair occurs when two candidates appear only in the same two cells within one row, column, or box.
Why is it called a Hidden Pair?
The two important candidates are hidden among extra candidates inside the pair cells.
Can a Hidden Pair appear in a 3×3 box?
Yes. Hidden Pairs can appear in rows, columns, and 3×3 boxes.
Does a Hidden Pair place a number directly?
Usually not. It removes extra candidates from the two pair cells and may reveal another solving step.
What is the difference between Hidden Pair and Naked Pair?
A Hidden Pair is found by tracking two candidates restricted to two cells. A Naked Pair is found by spotting two cells that already contain only the same two candidates.
Practise Finding Hidden Pairs
Open a Hard or Expert Sudoku puzzle, turn on Notes, and count candidate positions inside each row, column, and box.