16x16 sudoku: the giant grid
A 16x16 sudoku takes the classic puzzle and scales it up. Instead of 81 cells there are 256, split into sixteen boxes of 4×4. Each row, column and box must hold sixteen different symbols, once each. If a regular sudoku is a coffee break, a giant sudoku is an evening.
The puzzles here are generated fresh every time, with one solution and no guessing needed. They are set at a basic level of logic, because on a grid this size the challenge is stamina and order more than clever tricks.
How the symbols work
There are only nine single-character digits, so a 16x16 grid needs seven extra symbols. This game uses the digits 1 to 9, then the letters a to g:
| Symbol | 1–9 | a | b | c | d | e | f | g |
|---|---|---|---|---|---|---|---|---|
| Stands for | 1–9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
You do not need to think of the letters as numbers at all. They are just sixteen different marks, and no arithmetic is involved. To enter a letter, select a cell and press that letter key on your keyboard. Some books print 16×16 puzzles with 0 to 9 and A to F instead; the logic is identical.
Strategy for a 16x16 sudoku
The techniques are the same as in 9×9 sudoku. What changes is how you organise your attention.
- Sweep by symbol. Go through the symbols in a fixed order, 1 to g. For each one, look at every box where it is missing and check which rows and columns already block it. This catches most of the easy placements.
- Use the fullest lines. A row with fourteen symbols has two gaps. Find the two missing symbols, check their columns, and both cells often settle at once.
- Work box by box when you slow down. Pick the box with the most filled cells and ask, for each missing symbol, where it can go.
- Add notes sparingly. Full candidate lists for 256 cells would take longer than the solve itself. Add notes only where scanning stops working, and keep them updated.
- Check before you commit. A wrong symbol on a big grid can stay hidden for a long time. A quick look along the row, column and box before each entry saves a painful search later.
How long it takes
Most solvers need somewhere between 45 minutes and a few hours for one puzzle. Speed comes from routine: a fixed scanning order, fast recognition of the letters, and not losing your place. Many people solve a 16x16 sudoku in two or three sittings, and that is a perfectly good way to play.
Who it is for
Giant sudoku suits players who already enjoy hard sudoku and want something longer rather than trickier. If you would rather have tough logic on a normal grid, try expert sudoku. For an extra rule on the classic size, Sudoku X adds the two diagonals.
How to play here
Click a cell and type a digit or a letter from a to g. Right-click a cell for pencil marks. The board scales to fit your screen, and full screen gives you the largest cells, which helps a lot at this size.
How to play 16x16 Sudoku
- The grid has 16 rows, 16 columns and sixteen 4×4 boxes.
- Each row, column and box must contain all sixteen symbols exactly once.
- The symbols are the digits 1 to 9 and the letters a to g, where a stands for 10 and g for 16.
- The starting symbols are fixed. Every puzzle has one solution that logic alone can reach.
16x16 Sudoku tips
Work one symbol at a time
Pick one symbol, find every copy already on the board, and check the boxes where it is still missing. With sixteen boxes, a single sweep often places three or four copies at once.
Leave notes for later
Writing every candidate in 256 cells takes ages. Scan first, and only add notes to the box or row where you get stuck.
Take breaks and come back
A 16x16 sudoku is a long solve. Fresh eyes spot singles that tired eyes miss, and the puzzle will wait for you in the tab.
Frequently asked questions
How do you solve a 16x16 sudoku?
The same way as a 9×9. Scan for a symbol that has only one possible cell in a row, column or box, write it in, and repeat. The method does not change, there is just much more grid to cover, so work in a fixed order and stay patient.
What numbers are used in a 16x16 sudoku?
Sixteen symbols are needed, and only nine digits are single characters. Here the grid uses 1 to 9 and then the letters a to g. Some printed puzzles use 0 to 9 and A to F instead, but the rules are the same.
How long does a 16x16 sudoku take?
Expect anywhere from 45 minutes to a few hours, depending on your speed. That is several times longer than a 9×9 of similar difficulty.
Can I play 16x16 sudoku on a phone?
It works best on a computer with a keyboard, so you can type the letters a to g. The number pad on phones only has the digits 1 to 9.
