How to Play Killer Sudoku
Killer sudoku mixes sudoku with simple sums. Instead of many starting digits, the grid is split into cages (dashed outlines), each with a small number in its corner.
The rules
- Sudoku rules: every row, column and 3×3 box contains each digit 1 to 9 exactly once.
- Cage sums: the digits in a cage add up to the number in its top left corner.
- No repeats in a cage: a digit appears at most once in any cage.
Every cell is in exactly one cage. Some puzzles start with a few digits filled in; many start empty.
Cage combinations
The size and sum of a cage often tell you which digits must be in it:
| Cage | Digits |
|---|---|
| 2 cells, 3 | 1 + 2 |
| 2 cells, 17 | 8 + 9 |
| 3 cells, 6 | 1 + 2 + 3 |
| 3 cells, 24 | 7 + 8 + 9 |
| 4 cells, 10 | 1 + 2 + 3 + 4 |
| 4 cells, 30 | 6 + 7 + 8 + 9 |
The order inside the cage still has to come from the rest of the grid.
The 45 rule
Each row, column and box holds 1 to 9 once, so it adds up to 45. If the cages that lie wholly inside a box add up to 38, the one cell of that box that belongs to a cage poking out must be 7. The same works for several rows or columns together (90 for two, 135 for three).
On kawu
- Every puzzle has one solution and can be solved by logic, without guessing.
- Easy puzzles have small cages and a few starting digits; hard ones have bigger cages and few or none.
- Notes, erase, undo and hints work as in our sudoku. The daily puzzle is the same for everyone.
Frequently asked questions
Can a number repeat in a killer sudoku cage?
No. The digits inside a cage are all different, even when the cage spreads over two rows or boxes.
What is the 45 rule in killer sudoku?
Every row, column and 3×3 box contains 1 to 9 once, so its digits add up to 45. Add up the cages that lie wholly inside a row, column or box; the cells left over must make up the rest of 45.
Last updated 2026-10-19