An example 16×16 Sudoku (Hexadoku): sixteen symbols fill every row, column and 4×4 box (a few 1-9 shown).
16×16 Sudoku is the most common of the large formats: a sixteen-by-sixteen grid divided into 4×4 boxes, filled with sixteen different symbols. Those symbols are usually the numbers 1-16 or the hexadecimal characters 0-F. The rules are unchanged from Classic Sudoku - it is simply bigger, and it rewards patience far more than cleverness.
The rule: sixteen symbols per row, column and 4×4 box
Fill the grid so that every row, every column and every 4×4 box contains all sixteen symbols exactly once. A single 4×4 box already holds a full set - below, one box is filled with 1 through 16 to show the range you are working with.
One 4×4 box holds all sixteen symbols (here 1-16). The full grid has sixteen such boxes.
Numbers or hexadecimal
Two labelling schemes are common. Puzzles for a general audience use the numbers 1-16, which are unambiguous but make each cell two digits wide. Puzzles aimed at programmers use the sixteen hexadecimal characters 0, 1, 2 … 9, A, B, C, D, E, F, which keep every cell to a single character and give the grid its "Hexadoku" nickname. The logic is identical either way - the symbols are just labels for sixteen distinct values.
Patience over difficulty
A 16×16 is not conceptually harder than a 9×9 - it uses the same techniques - but there is far more to track: sixteen candidates per cell, 256 cells, and boxes four wide. Careful pencil-marking becomes essential, because a single missed elimination is easy to make and slow to find. The reward is a long, absorbing solve; treat it as a marathon, keep your candidate marks tidy, and work one unit at a time.
Solving strategy
- Pencil-mark methodically. With sixteen possible symbols per cell, candidate notes are not optional.
- Work box by box. Finish scanning one 4×4 box before moving on, to avoid losing your place.
- Hunt hidden singles per symbol. Take one symbol at a time and place it wherever it is confined to a single cell.
- Use the same techniques as 9×9. Naked pairs, hidden singles and X-Wings all scale up unchanged.
Common mistakes
- Sloppy candidate marks. On a grid this size, one wrong pencil mark can derail the whole solve.
- Forgetting a symbol. All sixteen values must appear - it is easy to overlook one when scanning.
- Mixing labelling schemes. Decide whether the grid uses 1-16 or 0-F and stick with it.
- Rushing. The 16×16 rewards steady, careful work far more than speed.
Can I play it here?
Not yet - Sudoku 16×16 isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Try the closely related Classic, which you can play right now.
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Sudoku 16×16 belongs to the size variant family and runs on 16×16. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.