Sudoku Hidden Pairs Explained: Learn to Solve Puzzles Faster

Hidden pairs is a basic Sudoku technique that lets you solve puzzles by eliminating candidates from the grid. Let’s take a look at what a hidden pair is and how it’s useful.

What is a hidden pair in Sudoku?

A hidden pair is when you have the same two digits pencil marked in precisely two cells within the same row, column, or block.

What makes them ‘hidden’ is that there is at least one other digit also pencil marked in at least one of these cells. (If there weren’t other digits and the pair was all by itself, it would make it a naked pair.)

Consider the hidden pair example below.

example of a hidden pair in a row — Hidden pair example

In this example where all the candidates are pencil-marked in, the digits 1 and 7 only appear within the same row in the 7th and 9th cells from the left. This makes the 1 and 7 a hidden pair.

Keep in mind that this isn’t limited to rows, but also works with columns and 3×3 blocks.

The hidden logic of hidden pairs

So how does this help you solve your Sudoku puzzle?

The power of hidden pairs is that they let you immediately eliminate all other candidates from the two cells the pair occupies.

In the case of the example above, this means we can eliminate the 8 from the 7th cell in the row and the 6 from the 9th cell.

This is because these are the only two cells in the row that can contain a 1 or a 7. We just don’t know which one is the 1 and which one is the 7 yet.

the same hidden pairs example with the extra candidates removed — Removing the 8 and 6 candidates

In this particular example, by using the hidden pairs strategy to eliminate candidates, we can place a new digit in the grid as there’s now a hidden single: the 8 in the first cell.

the 8 placed in thanks to the newly revealed hidden single — Placing an 8

This hopefully demonstrates the power of hidden pairs in helping you solve your Sudoku puzzles.

Just remember that hidden pairs can also occur in columns and 3×3 blocks. We’ve only looked at rows as one example. The exact same logic appears in the 3×3 block example below.

a 3x3 block example — Hidden pairs example in a 3×3 block

Other types of hidden subsets

Hidden pairs are only one type of what’s known as a hidden subset.

There are also hidden singles, hidden triples, and hidden quads. As you might guess, these names refer to how many digits you apply the same hidden logic to.