Sudoku Solver

Use this sudoku solver to find the solution for any valid sudoku puzzle. Enter the known digits, click Solve, and get the answer instantly. Want to understand how it was solved? Click Show steps to replay each move.

Solving techniques

The solver works systematically through three techniques in order of increasing complexity.

Naked Single

A naked single occurs when an empty cell has only one possible digit remaining after eliminating all digits already present in the cell's row, column, and 3×3 box. It is the fastest and most common solving technique, and it is sufficient to solve most beginner and easy puzzles.

Example: A cell in the centre box has digits 1, 2, 3, 4, 6, 7, 8, and 9 eliminated by its row, column, and box — the only remaining digit is 5. The cell must be 5 — a naked single.

Read more: Sudoku strategies

Hidden Single

A hidden single is a digit that can only fit in one cell within a particular row, column, or box — even though that cell appears to have multiple candidates. The digit is "hidden" among other candidates but is the only possible position for it within its group.

Example: Digit 7 is missing from box 1 (top-left). Of the five empty cells in the box, 7 is eliminated as a candidate from four of them by their rows and columns. Only one cell remains where 7 can go — a hidden single.

Read more: How to play sudoku for beginners

Naked Pairs

A naked pair occurs when exactly two cells in the same group (row, column, or box) share exactly the same two candidate digits and no others. Those two digits must go in those two cells in some order, which means they can be eliminated as candidates from every other cell in the group. This solver handles naked singles and hidden singles directly; naked pairs are handled automatically via backtracking when the simpler techniques are insufficient.

Read more about naked pairs and advanced techniques: Sudoku strategies

Further reading