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.
For a deeper look at the full rule set, see the Pointing Pairs strategy page.
How to Spot a Pointing Pair (Step-by-Step)
The scan is systematic. Work through each box one at a time:
- 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 as a candidate.
- 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 sit 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 — but only outside the current box. Never touch the cells inside the box.
- Move to the next digit, then the next box. Repeat until you have covered all nine boxes and all nine digits.
With practice this scan takes only a few seconds per box. The key habit is checking every digit in every box rather than scanning opportunistically.
Pointing Pairs vs Pointing Triples
The logic is identical whether two or three cells are involved:
- A pointing pair has exactly 2 aligned candidate cells in the box.
- A pointing triple has exactly 3 aligned candidate cells in the box.
Both allow the same elimination: remove the candidate from the rest of that row or column outside the box. Pointing triples are slightly rarer because a digit confined to three cells in one row of a box means every other row in the box already has the digit placed — but when they appear, the elimination power is the same.
If a candidate appears in 4 or more cells inside a box and they happen to align, no elimination is valid — check your pencil marks for an error.
Pointing Pairs vs Box-Line Reduction — Same Thing?
These two techniques are often confused because they are mirror images of each other. Both fall under the "Locked Candidates" family, but they start from opposite directions:
- Pointing Pairs (Type 1): start with the box. When a candidate inside a box is confined to one row or column, eliminate it from that row or column outside the box.
- Box-Line Reduction (Type 2): start with the row or column. When a candidate in a row or column only appears in cells belonging to one box, eliminate it from the rest of that box.
A useful mental shortcut: pointing pairs point outward from the box, while box-line reduction draws inward to the box. Neither is harder than the other — they are complementary. Always scan for both when you work through a grid.
Practice Example (Beginner-Friendly)
Consider Box 4 (the middle-left 3×3 box, covering rows 4–6 and columns 1–3). Suppose your pencil marks show that the digit 4 appears as a candidate only in two cells: row 4 col 2, and row 4 col 3.
Both cells are in row 4. That means 4 is a pointing pair locked to row 4 within Box 4.
Elimination: Remove 4 as a candidate from every cell in row 4 that lies outside Box 4 — that is, columns 4 through 9 of row 4. If any of those cells had 4 as a candidate, cross it out.
After that elimination, check whether any cell in row 4 now has only one candidate left. If so, you have just revealed a naked single — place that digit immediately and continue solving.
What Difficulty Level Uses Pointing Pairs?
Pointing pairs typically appear on Medium puzzles and above. Easy puzzles are usually solvable with naked and hidden singles alone. On Medium, the grid often stalls after singles are exhausted, and a pointing pair or two is enough to unlock the next batch of placements.
On Hard and Expert grids, pointing pairs remain useful but are rarely sufficient on their own. You will often need to combine them with naked pairs, hidden pairs, or more advanced techniques. That said, always scan for pointing pairs and box-line reduction first — they are fast to spot and regularly provide free eliminations even on harder puzzles.
Ready to practice? Try today's daily Sudoku and actively look for pointing pairs as you solve.
Frequently Asked Questions
What are pointing pairs in sudoku?
Pointing pairs occur when a candidate digit appears in only two or three cells within a box, and all those cells lie in the same row or column. That digit can then be eliminated from the rest of that row or column outside the box.
How do I spot a pointing pair?
For each box, look at a single candidate digit and check which cells it appears in. If all its appearances in that box align in one row or one column, you have a pointing pair or triple. Now eliminate that candidate from the rest of that row or column.
What is the difference between pointing pairs and locked candidates?
They are two names for the same logical pattern. Locked candidates is the general term; pointing pairs specifically describes the case where candidates in a box point to a row or column. Box-line reduction is the reverse: candidates in a row or column are confined to one box.