The idea
Look at a unit and count where each missing digit can go. If two different digits can each only go in the same two cells, those two cells must hold those two digits between them. Every other candidate in those two cells can be struck out.
The elimination happens inside the two cells, not around them — that is what makes it the opposite of a naked pair.
Two digits share the same two possible cells in this unit, so every other candidate is cleared out of those cells.
Naked pair or hidden pair?
| Naked pair | Hidden pair | |
|---|---|---|
| What you notice | Two cells with the same two candidates | Two digits with the same two possible cells |
| What it eliminates | Those digits, elsewhere in the unit | Other candidates, inside the two cells |
| Extra candidates allowed? | No | Yes — that is what hides it |
How to find one
Take a unit and list, for each missing digit, the cells that can hold it. Any digit with exactly two possible cells is a candidate for the pattern; if two such digits share the same two cells, you have a hidden pair. It is slower to spot than a naked pair, which is why it is worth checking only when the quick moves have run out.
Why bother
Because a hidden pair usually turns two crowded cells into two cells with two candidates each — which is a naked pair, which then eliminates further. One hidden pair often unlocks a whole corner of a hard grid.
Common questions
What is a hidden pair in Sudoku?
Two digits that can only go in the same two cells of a unit. Those cells must hold those digits, so all their other candidates can be removed.
How is it different from a naked pair?
A naked pair eliminates outside the two cells; a hidden pair eliminates inside them. A naked pair is visible immediately, a hidden one has to be counted out.
Do hidden triples exist?
Yes, with three digits confined to three cells. They are rare and hard to spot, and no puzzle on this site requires one.