Ready to graduate from the standard 9×9 grid? Welcome to the world of Sudoku Mega 16×16. Also known as “Hexadoku” or “Monster Sudoku,” this supersized puzzle takes the logic you love and expands it into a massive 16×16 grid. It is the ultimate test of patience, pattern recognition, and deduction.

If you find standard puzzles too easy, our free Mega Sudoku tool above is designed to push your brain to the limit.

What is Hexadoku?

Hexadoku is a 16×16 variation of Sudoku. Because a 16×16 grid requires 16 distinct symbols (and we only have 10 digits), this version typically introduces letters to fill the gap.

While the logic remains identical to the classic game, the scale is much larger:

• The Grid: A massive 256 cells (16 rows by 16 columns).
• The Symbols: Uses numbers 0-9 and letters A-F (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F).
• The Blocks: Instead of 3×3 squares, you are working with sixteen 4×4 regions.

Rules of 16×16 Sudoku

The rules for Sudoku Mega 16×16 are simple extensions of the classic game rules.

1. Rows and Columns: Every horizontal row and vertical column must contain all 16 symbols (0-9 and A-F) exactly once. No repeats allowed.
2. 4×4 Regions: The grid is divided into 16 smaller 4×4 boxes (outlined in bold). Each of these boxes must also contain every symbol from 0 to F exactly once.
3. The Golden Rule: Logic only! You never have to guess. There is always a logical path to the solution.

3 Expert Tips for Solving Mega Sudoku

Jumping from 81 cells to 256 cells is a big leap. Here is how to keep your grid organized and solve Hexadoku like a pro.

1. Use “Pencil Marks” Aggressively

In a standard 9×9 puzzle, you might be able to keep numbers in your head. In a 16×16 Sudoku, that is nearly impossible. Use the “Note” or “Pencil” feature to mark down candidates. If a cell can only be a ‘4’, ‘A’, or ‘F’, write them down. As you solve other parts of the 4×4 block, you can eliminate these candidates one by one.

2. Hunt for the “Hidden Singles”

With 16 numbers to track, it is easy to miss the obvious. Scan the rows and columns that are almost full. If a row has 15 filled cells, the last one is a “naked single”—an easy win. In Mega Sudoku, these are often hidden in plain sight because the grid is so visually busy.

3. Focus on One Block at a Time

Don’t try to solve the whole board at once. Pick one specific number or letter (like ‘A’) and cross-hatch the entire board to see where it must go in each 4×4 region. Repeating this process for all 16 symbols is the most reliable way to break into a hard puzzle.

Think you have what it takes? Scroll up to the top of the page and start your first Sudoku Mega 16×16 game now!