About Killer Sudoku
Killer Sudoku is sudoku with arithmetic. The grid follows the usual rules: every row, column and 3×3 box holds 1 to 9 once. On top of that, dashed cages group squares together, and the digits in each cage must add up to the small total in its corner, with no digit repeated inside a cage. Every killer puzzle here starts with an empty grid: the sums are the clues.
How to play Killer Sudoku
- Every row, column and 3×3 box contains 1 to 9 exactly once.
- The digits in a cage add up to the number in the cage's corner.
- A digit cannot repeat within a cage, even when the cage crosses boxes.
- Start from cages that have only one possible combination, then use the totals of whole rows and boxes to place the rest.
Where to start
Some cages can only be filled one way, and they are the place to begin.
| Cage | Total | Only possible digits |
|---|---|---|
| 2 squares | 3 | 1 and 2 |
| 2 squares | 17 | 8 and 9 |
| 3 squares | 6 | 1, 2 and 3 |
| 3 squares | 24 | 7, 8 and 9 |
| 4 squares | 10 | 1, 2, 3 and 4 |
| 4 squares | 30 | 6, 7, 8 and 9 |
The other key fact: every row, column and box adds up to 45. If the cages inside a box cover all but one square, that square is 45 minus their totals. More on both in Killer sudoku rules.
Difficulty
Easy to Expert changes how much the cages give away. Easy puzzles have more cages, many of them small, some a single square whose total is simply its digit. Expert puzzles have fewer, larger cages of up to five squares with many possible combinations, so more of the work is the 45 rule and ruling digits out.
Controls
- Select a square, then use the number pad or keyboard.
- N toggles notes, Backspace erases, H gives a hint, U or Ctrl/Cmd+Z undoes.
- Progress and notes are saved for each variant separately.
Scoring
| Level | Base | Speed bonus, up to | Per mistake | Per hint |
|---|---|---|---|---|
| Easy | 1,000 | 250 | −100 | −250 |
| Medium | 2,000 | 500 | −200 | −500 |
| Hard | 3,500 | 875 | −350 | −875 |
| Expert | 5,000 | 1,250 | −500 | −1,250 |
Only fully solved puzzles are ranked. Your score is the difficulty base plus a speed bonus of at most 25% of that base. The bonus falls by 0.5 points per elapsed second, rounded to the nearest whole point, and never below zero. Each mistake deducts 10% of the base; each hint deducts 25%. A solved puzzle always earns at least 10% of its base. Undo does not refund time, mistakes or hints. Each Sudoku variant has its own leaderboard. Existing scores remain on the same boards; new solves use this formula.
