Killer Sudoku rules
Fill the grid so that every row, column and 3x3 box contains 1 to 9 exactly once, just like Sudoku.
The grid is split into cages (dotted outlines). The small number in each cage is the sum of its cells.
A number can't repeat inside a cage.
There are no given numbers. Everything comes from the sums.
How to start a Killer Sudoku
Look for cages with only one possible set of numbers. A 2-cell cage of 3 must be 1 and 2; a 2-cell cage of 17 must be 8 and 9.
Use the rule of 45: every row, column and box adds up to 45. If the cages inside a box add up to 38 and one cell is left over, that cell is 7.
Mix in normal Sudoku: once a 1 and 2 are locked into a cage, no other cell in that row or box can be 1 or 2 if the cage sits in it.
Levels
| Level | What to expect |
|---|
| Easy | Cages up to 4 cells. Solvable without guessing |
| Medium | Cages up to 5 cells. Solvable without guessing |
| Hard | Cages up to 6 cells. Needs deeper reasoning |
| Expert | Cages up to 7 cells. The hardest level |
Cages with only one combination
Memorize these. They are the easiest way into any Killer Sudoku.
| Cells | Sum | Must be |
|---|
| 2 | 3 | 1 + 2 |
| 2 | 4 | 1 + 3 |
| 2 | 16 | 7 + 9 |
| 2 | 17 | 8 + 9 |
| 3 | 6 | 1 + 2 + 3 |
| 3 | 7 | 1 + 2 + 4 |
| 3 | 23 | 6 + 8 + 9 |
| 3 | 24 | 7 + 8 + 9 |
| 4 | 10 | 1 + 2 + 3 + 4 |
| 4 | 11 | 1 + 2 + 3 + 5 |
| 4 | 29 | 5 + 7 + 8 + 9 |
| 4 | 30 | 6 + 7 + 8 + 9 |
| 5 | 15 | 1 + 2 + 3 + 4 + 5 |
| 5 | 16 | 1 + 2 + 3 + 4 + 6 |
| 5 | 34 | 4 + 6 + 7 + 8 + 9 |
| 5 | 35 | 5 + 6 + 7 + 8 + 9 |
| 6 | 21 | 1 + 2 + 3 + 4 + 5 + 6 |
| 6 | 22 | 1 + 2 + 3 + 4 + 5 + 7 |
| 6 | 38 | 3 + 5 + 6 + 7 + 8 + 9 |
| 6 | 39 | 4 + 5 + 6 + 7 + 8 + 9 |
| 7 | 28 | 1 + 2 + 3 + 4 + 5 + 6 + 7 |
| 7 | 29 | 1 + 2 + 3 + 4 + 5 + 6 + 8 |
| 7 | 41 | 2 + 4 + 5 + 6 + 7 + 8 + 9 |
| 7 | 42 | 3 + 4 + 5 + 6 + 7 + 8 + 9 |
FAQ
Is Killer Sudoku harder than Sudoku?
It starts with an empty grid, so it can feel harder at first. With the unique combinations and the rule of 45, Easy and Medium puzzles are very approachable.
Does every puzzle have one solution?
Yes. Each puzzle is checked by a program to have exactly one solution, twice: when it's made and again before it's published.
Do I need to guess?
Not on Easy and Medium: every puzzle there is checked to be solvable without guessing, using cage combinations, the rule of 45 and basic Sudoku logic. Hard and Expert need deeper reasoning.
Is it free?
Yes. Every level is free and unlimited. No sign-up.
