Naked pairs are one of the most frequently useful techniques in Sudoku. Once you understand how they work, you'll see them in almost every medium and hard puzzle — and eliminating candidates through them often unlocks cells that seemed completely stuck.
Two cells in the same row, column, or box that each contain exactly the same two candidates — and only those two. No other candidates appear in either cell.
Cells B and C both contain only {3, 7}. That's a naked pair. One of them will be 3, the other will be 7 — we don't know which yet. But we know 3 and 7 cannot appear anywhere else in row 4. Remove them from cells A and D (and any other cell in row 4 that has 3 or 7 as a candidate).
The two digits in the pair must each go in one of the two cells. There's no room for them anywhere else in the unit. If any other cell in the same unit had 3 or 7, it would create a contradiction — you'd have no valid placement for one of the pair digits.
Scan for cells with exactly two candidates. When you find one, look in the same row, column, and box for another cell with the identical pair. If you find it, eliminate both digits from the rest of that shared unit.
Important: both cells must have exactly two candidates, and they must be the same two. A cell with candidates {3, 7, 9} doesn't form a naked pair with a cell that has {3, 7}.
The same logic applies inside a 3×3 box. Two cells anywhere in the box with identical two-candidate sets form a naked pair for that box. Eliminate both digits from all other cells in the box.
{1,3} appears in two cells (row 2 col 1 and row 3 col 2). Naked pair — eliminate 1 and 3 from the third cell in row 1 ({1,3,5,6} becomes {5,6}) and from the bottom-right cell ({2,4,7} is unchanged since it doesn't contain 1 or 3).
The same idea scales up. Three cells in a unit that together contain only three distinct candidates form a naked triple. The three digits can only go in those three cells — eliminate them from the rest of the unit.
The cells don't each need to have all three candidates. {1,2}, {2,3}, {1,3} is a valid naked triple. So is {1,2,3}, {1,2}, {3}.
After removing candidates through a naked pair, always rescan the affected units. Eliminations often trigger hidden singles — cells where only one candidate remains after the reduction. This chain reaction is how hard puzzles gradually open up.
Medium Sudoku puzzles are the ideal difficulty for training naked pair recognition.
Play Medium Sudoku →