When three numbers can only exist in three particular cells within a unit, all other candidates in those cells can be removed.
A Hidden Triple exists when three candidate numbers within a row, column, or 3x3 box can only be placed in exactly three cells. These cells may contain other candidates as well, but the three "hidden" numbers are locked into those three cells. Since those three numbers must occupy those three cells, all other candidates can be safely removed from them.
For example, in a box where the numbers 1, 6, and 8 only appear as candidates in cells A, B, and C - even though cell A has [1, 3, 6, 9], cell B has [1, 6, 8], and cell C has [4, 6, 8] - the numbers 1, 6, and 8 form a Hidden Triple. You can eliminate 3 and 9 from cell A, and 4 from cell C, leaving just the triple candidates in each cell.
Not every cell in the triple needs to contain all three numbers. As long as each of the three numbers only appears within those three cells in the unit, the Hidden Triple is valid. Explore related terms in our Sudoku glossary.
Hidden Triples are typically needed in hard and expert Sudoku puzzles when singles, pairs, and simpler intermediate techniques have been exhausted. They are more complex to find than Hidden Pairs but follow the same underlying logic.
Before searching for Hidden Triples, make sure you have checked for all Pointing Pairs and Box-Line Reductions, as these simpler techniques may resolve the grid without needing triples. See our strategies overview for the recommended solving order, and how to play Sudoku for fundamentals.
Hidden Triples is classified as an intermediate-level technique, though it sits at the upper end of intermediate complexity. Finding them requires systematic analysis rather than quick visual scanning.
Not needed - simpler techniques are sufficient
Very rarely needed
Occasionally needed for stubborn puzzles
Useful as part of a comprehensive solving approach
A Hidden Triple occurs when three candidate numbers can only appear in exactly three cells within a row, column, or 3x3 box. Those three cells may contain additional candidates, but since the three numbers are restricted to those cells, all other candidates can be removed from them.
In a Naked Triple, three cells collectively contain only three candidates total. In a Hidden Triple, the cells may have additional candidates, but three specific numbers are confined to those three cells within the unit. The elimination is different: Naked Triples remove candidates from OTHER cells, while Hidden Triples remove candidates from the TRIPLE cells themselves.
Hidden Triples are less common than Hidden Pairs but appear in hard and expert puzzles. They require careful analysis of candidate distributions within a unit. Many solvers find them by methodically counting where each candidate can go within a row, column, or box.
Hidden Triples are challenging because you must track three different numbers simultaneously across a unit. Additionally, each cell in the triple may contain other candidates that obscure the pattern. Systematic analysis with pencil marks is essential for finding them.
Generally, check for Pointing Pairs and Box-Line Reduction first, as they are easier to spot and may simplify the grid enough to reveal Hidden Triples or make them unnecessary. Apply techniques from simplest to most complex for maximum efficiency.
Track three digits in row 1: 1, 5, and 7. Where can each one go? Each fits only in cells C1, C2, and C3.
Step 1 of 3 — full interactive demo available with JavaScript enabled
Ready to put your skills to the test?
Try Final Sudoku - an ad-free Sudoku experience with smart tools