All Sudoku Variants
15×15 · Size Variant

Sudoku 15×15

A 15×15 grid with 3×5 boxes using the digits 1–15.

1 2 3 4 5 6 7 8 9

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.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 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: