16x16 Sudoku Solver

16x16 Sudoku Solver: solve larger Sudoku puzzles online

Use this free 16x16 Sudoku Solver when a standard 9x9 solver is not enough. A 16x16 Sudoku has 256 cells, sixteen rows, sixteen columns, and sixteen 4x4 boxes. The symbols are 1-9 followed by 10-16, so every row, column, and box must contain each symbol exactly once.

The tool follows the same workflow as our classic Sudoku solver: click a cell, enter the clues from your puzzle, then solve the grid, step through the answer, or export the puzzle string. It also checks whether your givens lead to a unique solution or whether multiple completed grids are possible.

How to use the 16x16 Sudoku solver

1. Copy the given symbols from your puzzle into the grid.
2. Use 10-16 for the extra symbols after 9.
3. Leave unknown cells blank, or import a 256-cell puzzle using 0 or . for blanks.
4. Press Solve for the full solution or Step to reveal one cell at a time.
5. Read the uniqueness message to see whether the puzzle has one answer or several.

16x16 Sudoku rules

The rules are familiar, but the grid is larger. Each row must contain 1-16 with no repeats. Each column must do the same. Each 4x4 box also contains the same sixteen symbols. Because the boxes are rectangular rather than square, checking the box boundaries is the most common place to make an entry mistake.

Why use a dedicated 16x16 solver?

A 16x16 puzzle has more cells and more candidates than a 9x9 puzzle, so a solver designed for 9x9 cannot validate the symbols or the 4x4 box layout correctly. This page is built specifically for 16x16 Sudoku, including import/export, keyboard entry for A-G compact symbols, contradiction checks, and solution counting.

Import format for a 16x16 Sudoku puzzle

If you already have the puzzle in text form, paste a 256-cell puzzle into the import box. Read the grid from left to right and top to bottom. Use separated values 1-16, or A-G as compact values for 10-16, and use 0 or . for empty cells. This format is useful when you are sharing a puzzle, checking a puzzle from another site, or saving a difficult 16x16 Sudoku for later.

How the solver checks a puzzle

The solver first validates rows, columns, and 4x4 boxes for duplicate symbols. It then searches the puzzle using candidate filtering and a best-empty-cell strategy, which means it chooses the cell with the fewest legal values before branching. After it finds a completed grid, it checks for a second solution so you know whether the puzzle is well formed.

Tips for entering 16x16 Sudoku clues

• Check the 4x4 box borders carefully; they are easier to misread than 9x9 boxes.
• Use the keyboard for fast entry: 1-9 and A-G work.
• If the solver reports multiple solutions, add more givens or review the puzzle source.
• If it reports no solution, look for a repeated symbol in a row, column, or box.

16x16 Sudoku Solver FAQ

What symbols does a 16x16 Sudoku use?

This solver uses 1-16. Every row, column, and 4x4 box must contain all sixteen symbols once.

Can a normal Sudoku solver solve 16x16 puzzles?

No. A normal 9x9 Sudoku solver uses nine symbols and 3x3 boxes, so it cannot validate a 16x16 puzzle correctly.

Does this solver prove uniqueness?

Yes. After solving, it counts solutions up to two and reports whether the puzzle has one solution or multiple solutions.