Killer Sudoku Online
Sudoku with a dash of math: instead of given numbers, the grid is split into dotted cages, each showing its sum.
How to play Killer Sudoku
The classic Sudoku rules apply: every row, column and 3×3 box must contain the numbers 1 to 9 with no repeats. The difference is that the grid starts out empty and is divided into cages, groups of cells with a dotted outline.
The small number in the corner of each cage is the sum of its cells, and no number can repeat inside the same cage. A two-cell cage with a sum of 3, for example, can only hold 1 and 2; one with a sum of 17 can only hold 8 and 9.
Start with cages that have very low or very high sums, since they have few possible combinations, and remember that every row, column and box adds up to 45. Use “Notes” (or the N key) to mark candidates; with “Show conflicts” on, repeated numbers and cages with the wrong sum turn red.
Frequently asked questions
Why doesn’t Killer Sudoku start with any numbers?
Because the cage sums already give you all the information you need. Every grid here is checked by a solver to make sure it has exactly one solution using the cages alone.
What’s the rule of 45 trick?
Every row, column and 3×3 box adds up to 45 (1 + 2 + … + 9). If you add up the cages that fit entirely inside a box and one cell is left over, that cell equals 45 minus that total, which cracks open lots of puzzles.
What’s the difference between the levels?
On easy, cages are small, just 2 or 3 cells, with few possible combinations. On medium and hard you’ll find bigger cages of up to 5 cells that take more math and elimination.