An example 15×15 Sudoku: fifteen symbols fill every row, column and 3×5 box (a few 1-9 shown).
15×15 Sudoku is a fifteen-by-fifteen grid divided into 3×5 boxes, filled with the values 1-15. Each row, column and box must hold all fifteen once. It is a large, absorbing format for solvers who want more than the 9×9 without jumping all the way to a 16×16 or 25×25.
The rule: 1-15 in every row, column and 3×5 box
Fill the grid so no value repeats in any row, any column or any 3×5 box (three cells tall, five wide). One box already holds a full set - below, a 3×5 box is filled with 1 through 15.
One 3×5 box holds all fifteen values (1-15). The full grid has fifteen such boxes.
Same logic at a bigger scale
Nothing about the technique changes - a 15×15 uses the same singles, pairs and fish as a 9×9 - but with 225 cells and fifteen candidates each, there is far more to track. Tidy pencil-marks become essential, and the solve is longer and more meditative. A single missed elimination can be slow to spot, so work one unit at a time.
Numbers past nine
Because values run to 15, cells can be two characters wide (10-15). Some puzzles use letters or other symbols to keep every cell single-width, but the logic is identical - the symbols are just labels for fifteen distinct values.
Solving strategy
- Pencil-mark methodically. Fifteen candidates per cell make notes non-optional.
- Work box by box. Finish scanning one 3×5 box before moving on.
- Hunt hidden singles per value. Take one value at a time across the grid.
- Use the same techniques as 9×9. Every method scales up unchanged.
Common mistakes
- Expecting square boxes. The boxes are 3×5 rectangles - check the borders first.
- Forgetting a value. All fifteen must appear in each unit; the high numbers are easy to miss.
- Sloppy candidate marks. On a grid this size, one wrong mark can derail the solve.
- Rushing. The 15×15 rewards patience over speed.
Can I play it here?
Not yet - Sudoku 15×15 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 15×15 belongs to the size variant family and runs on 15×15. 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.