Pointing Pairs in Sudoku: How to Spot and Use This Key Elimination Technique
Pointing pairs are one of the first intermediate Sudoku techniques worth learning. Once you have exhausted naked and hidden singles, a pointing pair is often the move that breaks a stalled grid. This guide explains what pointing pairs are, how to find them quickly, and how they relate to box-line reduction — a technique often confused with them.
What Are Pointing Pairs in Sudoku?
A pointing pair occurs when a candidate number appears in only two cells within a 3×3 box, and those two cells share the same row or column. Because the number must go in one of those two cells, it is effectively "locked" to that row or column inside the box. That lock lets you eliminate the same candidate from every other cell in the same row or column outside the box.
In formal Sudoku terminology this is called Locked Candidates Type 1. The name "pointing pair" comes from the idea that the two candidate cells point outward — along a row or column — to signal where eliminations can be made.
Worked example: Say digit 4 can only go in two cells within the top-right box, and both cells happen to be in row 2. Wherever else a 4 appears as a candidate in row 2 — but outside that box — you can safely erase it. The 4 is locked inside that box's row-2 cells. This single move can trigger a cascade of new singles.
How to Spot a Pointing Pair (Step by Step)
- Pick one 3×3 box. Focus only on that box for now.
- Choose a candidate digit (1–9). Check which cells in the box still contain that digit.
- Count and check alignment. If the digit appears in exactly 2 (or 3) cells and those cells all sit in the same row, or all in the same column, you have found a pointing pair (or pointing triple).
- Eliminate along the pointing line. Remove that candidate from every other cell in that row or column — only outside the current box.
- Move to the next digit, then the next box. Pointing pairs often appear in clusters — solving one may reveal another.
Pointing Pairs vs Pointing Triples
The logic is identical whether two or three cells are involved. If a candidate appears in exactly three cells within a box and all three share the same row or column, that is a pointing triple. The elimination scope is the same: remove the candidate from the rest of that row or column outside the box.
Pointing triples are slightly harder to spot because three aligned cells can look coincidental. Training yourself to count candidate positions within each box — rather than scanning cells visually — is the fastest way to catch them.
Pointing Pairs vs Box-Line Reduction — Same Thing?
Almost. They are two directions of the same underlying logic, which is why some solvers call both "locked candidates."
- Pointing pairs (Type 1): start with the box. Candidates confined to one row or column inside a box eliminate from the rest of that row or column.
- Box line reduction (Type 2): start with the row or column. Candidates confined to one box inside a row or column eliminate from the rest of the box.
Mastering both directions doubles your detection rate on stuck grids.
Practice Example
Box 4 (rows 4–6, columns 1–3). Digit 4 appears as a candidate only in: row 4 col 2, and row 4 col 3. Both cells are in row 4 → pointing pair locked to row 4.
Elimination: Remove 4 from columns 4–9 of row 4 (outside Box 4). If a cell in row 4 now has one candidate left, place that digit (naked single).
What Difficulty Level Uses Pointing Pairs?
Pointing pairs typically appear on medium and hard puzzles. On easy grids, naked and hidden singles usually suffice. On expert and master puzzles, pointing pairs are often a prerequisite before more advanced techniques like hidden pairs become relevant.
If you find yourself frequently needing pointing pairs, you are ready to step up to harder difficulty — try a hard daily puzzle on Sudoku a Day and see how quickly you can apply them.
Common Mistakes
- Eliminating inside the box. Pointing pairs eliminate from outside the box along the shared row or column — not from the other cells inside the box itself.
- Partial alignment. If the candidate cells are not all in the same row or column, no pointing pair exists. Two cells diagonal to each other do not qualify.
- Skipping follow-up. After each elimination, re-scan for naked singles before moving on. Pointing pairs often immediately reveal a forced digit nearby.
Frequently Asked Questions
What are pointing pairs in Sudoku?
A pointing pair occurs when a candidate digit appears in only two cells within a 3×3 box, and both cells are in the same row or column. Because the digit must go in one of those two cells, it can be eliminated from all other cells in that row or column outside the box.
What is the difference between pointing pairs and box line reduction?
They are two directions of the same logic. Pointing pairs work from the box outward — candidates confined to one row or column inside a box eliminate from the rest of that row or column. Box line reduction works from the row or column inward — candidates confined to one box inside a row or column eliminate from the rest of the box.
What is a pointing triple?
A pointing triple follows the same logic as a pointing pair but with three cells. If a candidate appears in exactly three cells within a box and all three share the same row or column, the digit can be eliminated from the rest of that row or column outside the box.
When should I use pointing pairs?
Use pointing pairs after exhausting all naked and hidden singles. They are usually the next technique to try before moving on to pairs and triples. On medium, hard, and expert puzzles they appear regularly.