Sudoku Candidate Strategy
Hidden Triple Sudoku: How to Find and Use Hidden Triples
Learn how three candidate numbers can become locked inside the same three cells of a row, column, or box. Once you identify a Hidden Triple, remove every other candidate from those three cells.
3 Candidates, 3 Cells
If three numbers can appear only within the same three cells of one unit, those cells are reserved for those three numbers.
Choose Three Candidates
Look for three numbers with only a few remaining positions inside one Sudoku unit.
Find Three Shared Cells
All possible positions for those three candidates must be contained within the same three cells.
Remove Extra Candidates
Delete every candidate other than the three Hidden Triple numbers from those three cells.
What Is a Hidden Triple in Sudoku?
A Hidden Triple is a Sudoku candidate technique where three numbers can appear only in the same three cells within one row, column, or 3×3 box.
The three cells may contain many pencil marks, which is why the triple is called hidden.
What matters is not how many candidates are written inside the cells. What matters is where the three selected numbers are allowed to appear.
If candidates 2, 5, and 8 have no possible locations anywhere else in the unit, those three numbers must occupy those three cells in some order.
Therefore, any other candidate written inside those three cells can be removed.
The Hidden Triple Rule
Three Candidates Restricted to Three Cells
Inside one row, column, or box, choose three candidates — for example 2, 5, and 8.
If every possible occurrence of 2, 5, and 8 in that unit is contained within the same three cells, those three cells must contain 2, 5, and 8.
Remove all candidates other than 2, 5, and 8 from those three cells.
Why Is It Called a Hidden Triple?
A Hidden Triple can be difficult to notice because the three cells often contain several unrelated candidates.
Before the Hidden Triple
The candidates 2, 5, and 8 may be difficult to notice because candidates 4, 7, and 6 make the cells look crowded.
If 2, 5, and 8 appear nowhere else in that unit, they form a Hidden Triple.
How to Find a Hidden Triple
Choose One Sudoku Unit
Work with one row, one column, or one 3×3 box at a time.
Look for Restricted Candidates
Pay attention to candidates that appear only two or three times inside the selected unit.
Select Three Candidates
Find three candidate numbers whose combined possible positions occupy no more than three cells.
Confirm the Same Three Cells
Make sure those three candidates cannot appear anywhere else in the row, column, or box.
Ignore Extra Pencil Marks
The three cells may contain other candidates. Those extra candidates do not stop the Hidden Triple from existing.
Remove the Extra Candidates
Keep only the three Hidden Triple candidates inside the three cells and remove all unrelated candidates.
Rescan the Puzzle
The eliminations may reveal a single, pair, Locked Candidate, or another solving technique.
Hidden Triple Example
Suppose you are examining one Sudoku row and candidates 2, 5, and 8 appear only in three cells.
Assume candidates 2, 5, and 8 do not appear in any other unsolved cell in row 4.
Those three numbers must therefore occupy R4C2, R4C5, and R4C8 in some order.
Remove candidate 4 from R4C2, candidate 7 from R4C5, and candidate 6 from R4C8.
Why the Hidden Triple Elimination Works
A row, column, or box must eventually contain each number from 1 to 9 exactly once.
If three candidate numbers have only three possible cells available in that unit, those three cells are completely reserved for those three numbers.
The Key Logic
Three numbers need three positions, and only those three positions are available.
If one of those cells contained an unrelated fourth candidate, there would not be enough cells remaining for all three Hidden Triple numbers.
Therefore, the unrelated candidates can be safely removed.
Hidden Triples Can Appear in Rows, Columns, and Boxes
Row
Three candidates are restricted to three cells in one horizontal row.
Column
The same rule works when three candidates are restricted to three cells in one column.
3×3 Box
A Hidden Triple can also occur completely inside one 3×3 Sudoku box.
Do All Three Candidates Need to Appear in Every Cell?
No. This is one of the most common misunderstandings about Hidden Triples.
A Valid Pattern Could Look Like This
Candidates 2, 5, and 8 still occupy only those three cells as a group.
The important condition is that all possible positions for the three selected candidates remain inside those same three cells.
Hidden Triple vs. Hidden Pair
If Hidden Triples feel difficult, first review our Hidden Pair Sudoku guide . The underlying idea is the same, but a Hidden Triple adds one more candidate and one more cell.
Hidden Triple vs. Naked Triple
Easy Way to Remember
Hidden Triple: focus on where the three numbers can go.
Naked Triple: focus on what candidates the three cells contain.
Hidden Triple vs. Locked Candidates
For another candidate-restriction strategy, read our Locked Candidates Sudoku guide .
When Should You Look for a Hidden Triple?
Candidates Have Few Positions
A Hidden Triple is easier to find when several candidates appear only two or three times within a unit.
After Searching for Hidden Pairs
If you almost find a Hidden Pair but three candidates are involved, check whether the positions form a Hidden Triple.
Crowded Pencil Marks
Hidden Triples are especially useful when unsolved cells contain many candidates and obvious Naked Sets are difficult to see.
Hard Sudoku Puzzles
Hidden Triples often become useful after basic singles, pairs, and simpler candidate eliminations have been exhausted.
When Is It Not a Hidden Triple?
❌ One Candidate Appears in a Fourth Cell
If one of your three selected numbers can also appear in another cell in the same unit, the three candidates are not restricted to the triple.
❌ Four Cells Are Needed
A Hidden Triple requires the combined positions of the three candidates to fit within exactly three cells.
❌ Candidates Come From Different Units
The three cells must all belong to the same row, column, or box being analyzed.
❌ You Remove the Triple Candidates
The Hidden Triple candidates must remain in those three cells. Remove only the unrelated candidates from the triple cells.
Common Hidden Triple Mistakes
❌ Looking Only for Identical Candidate Lists
The three cells do not need to contain identical candidates. The restriction is about the three selected numbers and where they can appear.
❌ Confusing Hidden Triple With Naked Triple
Hidden Triples remove extra candidates from the three triple cells. Naked Triples remove the triple candidates from other cells.
❌ Forgetting to Check the Entire Unit
Always confirm that the three candidate numbers do not appear elsewhere in the selected row, column, or box.
❌ Searching Every Combination Randomly
Start with candidates that already have only two or three positions. This makes Hidden Triples much easier to find.
How to Practise Hidden Triples
1. Learn Hidden Pairs First
Hidden Triple uses the same restriction concept as Hidden Pair, but with three candidates and three cells.
2. Work One Unit at a Time
Scan one row, column, or box instead of trying to analyse the entire Sudoku grid at once.
3. Count Candidate Positions
Look first at candidates that appear only two or three times in the unit.
4. Group Three Candidates
Check whether three restricted candidates use only three cells between them.
5. Remove Only the Extra Candidates
Keep the three Hidden Triple numbers and delete unrelated pencil marks from the same cells.
6. Rescan After Every Elimination
Cleaning the three cells may reveal a Hidden Pair, Naked Pair, single, Locked Candidate, or another useful pattern.
Hidden Triple Practice Checklist
- 1. Are all three cells inside the same row, column, or box?
- 2. Have you selected exactly three candidate numbers?
- 3. Are all possible positions for those numbers contained within the same three cells?
- 4. Did you check that none of the three candidates appears elsewhere in that unit?
- 5. Did you remember that each cell does not need all three candidates?
- 6. Are there unrelated candidates inside the three cells that can be removed?
- 7. Are you keeping all valid Hidden Triple candidates?
- 8. Did you avoid removing the triple candidates from other cells using Hidden Triple logic?
- 9. Did you rescan the puzzle after cleaning the cells?
Related Sudoku Learning Pages
👥 Hidden Pair Sudoku
Learn the simpler two-candidate version of the same hidden-set concept.
👯 Naked Pair Sudoku
Learn how two cells can reserve two candidates and eliminate them elsewhere in a unit.
🔒 Locked Candidates Sudoku
Use candidate restrictions between boxes, rows, and columns to create eliminations.
🧠 Advanced Sudoku Techniques
Explore advanced Sudoku strategies including hidden sets, fish patterns, wings, rectangles, coloring, and strong-link techniques.
✖️ X-Wing Sudoku
Move from candidate sets to a powerful single-candidate pattern across two rows and columns.
🎨 Simple Coloring Sudoku
Follow candidate strong links using two colors to find advanced logical eliminations.
Frequently Asked Questions
What is a Hidden Triple in Sudoku?
A Hidden Triple occurs when three candidates can appear only in the same three cells within a row, column, or 3×3 box. Those cells are reserved for the three candidates, allowing all other candidates in the cells to be removed.
How do you find a Hidden Triple?
Look for three candidate numbers with their combined possible locations restricted to exactly three cells in one Sudoku unit.
What is the difference between Hidden Triple and Naked Triple?
A Hidden Triple identifies three numbers restricted to three cells and removes other candidates from those cells. A Naked Triple identifies three cells containing only three candidates between them and removes those candidates from other cells in the unit.
Do all three candidates have to appear in every Hidden Triple cell?
No. A valid Hidden Triple may contain different combinations such as 2/5, 2/8, and 5/8. The important rule is that the three candidates are restricted to the same three cells as a group.
What candidates can I remove from a Hidden Triple?
Remove every candidate in the three cells that is not one of the three Hidden Triple numbers.
Is Hidden Triple difficult to find?
It is usually harder to spot than a Hidden Pair because you must track three candidates across three cells. Checking candidates with only two or three positions makes the pattern easier to find.
Practise Hidden Triples
Open a Medium or Hard Sudoku puzzle, turn on Notes, choose one row, column, or box, and look for three candidate numbers whose possible positions are restricted to the same three cells.