If you want to improve at medium and hard Sudoku, one of the most useful techniques to learn is Locked Pairs and Locked Triples. These patterns help you eliminate candidates and make progress when basic scanning is no longer enough.
Many Sudoku players first learn how to fill in notes, but the next step is learning how to use those notes properly. Locked Pairs and Locked Triples are a great example of that. They help you see when a small group of candidates is restricted to a specific part of the grid, which allows you to remove those candidates from other cells.
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What Are Locked Pairs and Locked Triples in Sudoku?
Locked Pairs and Locked Triples happen when a candidate, or a small group of candidates, is restricted to the same row or column within a single 3×3 box.
If a candidate can only appear in two cells inside one box, and both of those cells are in the same row, that candidate is locked into that row within the box. The same idea applies if the cells are in the same column. Because of that, the candidate can be removed from the rest of that row or column outside the box.
A Locked Triple works the same way, but with three cells instead of two.
In simple terms, this technique helps you use the relationship between a box and a line to eliminate candidates elsewhere.
Why Are Locked Pairs and Triples Important?
Locked Pairs and Triples are important because they create clean eliminations without guessing.
Once your notes are filled in, you need ways to reduce the number of candidates in the grid. This technique is one of the most reliable ways to do that. It helps you narrow the puzzle down and often reveals easier follow-up moves such as Hidden Singles or Naked Pairs.
That is why Locked Pairs and Triples are often considered core medium-level Sudoku techniques.
When Should You Use Locked Pairs and Triples?
You should use this technique after you have filled in notes and direct placement is no longer working.
It becomes useful when you notice that a candidate inside a 3×3 box appears only in one row or only in one column. That restriction is the signal. Once you see it, you can check the rest of that row or column outside the box and remove the same candidate there.
This is often one of the first elimination techniques players use after learning candidate notation.
How Do Locked Pairs and Triples Work?
The logic is straightforward.
Imagine that in one 3×3 box, the candidate 7 appears in only two cells, and both cells are in the same row. Because 7 must go in one of those two places, it cannot appear anywhere else in that row outside the box.
The same logic applies if a candidate appears in three cells instead of two, as long as all three are still confined to the same row or column inside that box.
The key idea is restriction. The box restricts the candidate to a line, and that restriction creates eliminations outside the box.
What Is the Difference Between Locked Pairs/Triples and Pointing Pairs/Triples?
These techniques are very closely related, and many players confuse them.
In practice, the logic is almost the same: a candidate is restricted to one row or column within a box, and that allows eliminations elsewhere. Some players use the names interchangeably, while others treat Pointing Pairs/Triples as the more common label.
For your readers, the important part is not the naming debate. The important part is understanding the elimination logic and recognizing the pattern on the grid.
If your Academy keeps these techniques as separate lessons or labels, that is fine, but the article should stay focused on the actual solving idea.
Do Locked Pairs and Triples Help With Hard Sudoku?
Yes, they do.
Locked Pairs and Triples are especially helpful in medium and hard Sudoku because they reduce candidate clutter. Hard puzzles often require several small eliminations before the next obvious move appears. This technique is one of the cleanest ways to create those eliminations.
It may not solve a puzzle by itself, but it often opens the door to the next important step.
What Do You Need Before Using Locked Pairs and Triples?
You need accurate notes.
Without candidate notes, it is very difficult to spot whether a number is restricted to two or three cells inside a box. That is why Filling in Notes usually comes before this technique in the learning process.
If your candidates are incomplete or outdated, you may miss the pattern or make the wrong elimination. So before using Locked Pairs and Triples, make sure your notes are clean and current.
What Is the Biggest Mistake Players Make With Locked Pairs and Triples?
The biggest mistake is forcing the pattern where it does not exist.
A candidate must be restricted to the same row or the same column within a single 3×3 box. If the cells are spread across different rows and columns, then the technique does not apply.
Another common mistake is eliminating candidates too aggressively. You should only remove the candidate from the rest of that row or column outside the box. You should not remove it from unrelated cells elsewhere in the puzzle.
Careful restriction is what makes this technique valid.
Are Locked Pairs and Triples a Medium or Hard Sudoku Technique?
They are usually considered a medium-level technique, but they remain useful in hard Sudoku too.
Many players first meet them in medium puzzles, where they help bridge the gap between basic solving and more advanced elimination. In hard puzzles, they still matter because they often combine with other techniques to create progress.
So the best way to think about them is this: they are an essential intermediate technique that remains useful even at higher levels.
What Should You Learn After Locked Pairs and Triples?
A good next step is learning related elimination techniques such as:
Naked Pairs and Naked Triples
Pointing Pairs and Triples
Block-Line Reduction
Hidden Pairs and Hidden Triples
These techniques all build on the same general skill: reading candidates carefully and spotting restrictions in the grid.
Once you understand Locked Pairs and Triples, many of these other patterns become easier to recognize.
FAQ
What are Locked Pairs in Sudoku?
Locked Pairs happen when a candidate is limited to two cells in the same row or column within one 3×3 box, allowing eliminations outside that box.
What are Locked Triples in Sudoku?
Locked Triples work the same way, but the candidate is limited to three cells instead of two.
When should I use Locked Pairs and Triples?
Use them after filling in notes, when direct placement stops working and you notice candidates restricted to one row or column inside a box.
Do Locked Pairs and Triples help with hard Sudoku?
Yes. They are useful for reducing candidates and creating follow-up moves in both medium and hard puzzles.
What is the difference between Locked Pairs and Pointing Pairs?
They are very closely related and often described in similar ways. The main thing that matters is the elimination logic created by a candidate being restricted within a box.
Final Thoughts
Locked Pairs and Triples are one of the most useful Sudoku techniques for players who want to move beyond easy puzzles. They help you turn candidate notes into real progress by showing where numbers cannot go.
Once you understand how restriction inside a box affects the rest of a row or column, the puzzle becomes easier to control. That is why this technique is such an important part of medium and hard Sudoku solving.
For the full visual lesson with examples, images, and explanation, see the Sudoku Academy tutorial:
See the full Locked Pairs/Triples lesson in the Sudoku Academy.