Rules
How to play Killer Sudoku
- Sudoku rules first. Every row, column and 3×3 box contains each digit from 1 to 9 exactly once.
- Cages add up. Each dashed outline is a cage. The small number in its top-left corner is the total of the digits inside.
- No repeats in a cage. A digit can appear only once in a cage, even when the cage crosses a box line.
- Givens are fixed. Some puzzles print one or more digits in bold. They are part of the solution and you start from them.
A Killer Sudoku usually starts with fewer digits than a classic puzzle, often none at all, because the cage sums carry the information instead.
Cheat sheet
Cage totals with only one combination
| Cells | Lowest totals | Highest totals |
|---|
| 2 | 3 = 1+2 · 4 = 1+3 | 16 = 7+9 · 17 = 8+9 |
|---|
| 3 | 6 = 1+2+3 · 7 = 1+2+4 | 23 = 6+8+9 · 24 = 7+8+9 |
|---|
| 4 | 10 = 1+2+3+4 · 11 = 1+2+3+5 | 29 = 5+7+8+9 · 30 = 6+7+8+9 |
|---|
Print this table with your first few puzzles; it settles most opening moves.
The levels
What Easy, Medium and Hard mean here
The level sets how big the cages are and how many digits are printed. Smaller cages have fewer possible combinations, so they are easier to pin down. Below is what the generator produced for 20 puzzles per level (seed SAMPLE, October 2026); every one of the 60 was confirmed to have exactly one solution.
| Level | Cages per puzzle | Average cage size | Largest cage | Printed digits |
|---|
| Easy | 29–35 | 2.6 cells | 5 | 6–10 (7.4 on average) |
|---|
| Medium | 24–30 | 2.9 cells | 6 | 1–3 (1.9 on average) |
|---|
| Hard | 21–26 | 3.4 cells | 6 | 0–2 (1.5 on average) |
|---|
Difficulty here comes from cage size and printed digits, not from a graded list of solving techniques, so two puzzles at the same level can feel different. If one is too hard for a group, change the seed.
Questions
Killer Sudoku FAQ
What is Killer Sudoku?
A Sudoku with extra outlines called cages. Each cage shows a small number: the digits inside it must add up to that number and may not repeat. The usual rules still apply: every row, column and 3×3 box holds 1 to 9 once.
Does every Killer Sudoku here have exactly one solution?
Yes. After the cages are drawn, a solver that understands cage sums counts the solutions and stops at two. If it finds two, a digit where they differ is printed as a starting digit and the check runs again. The batch check under the preview shows the result for every puzzle.
Why do some puzzles have printed digits?
Some cage layouts allow more than one answer. Instead of discarding them, the generator prints one or two digits that remove the ambiguity. Easy puzzles get a few extra starting digits on purpose.
How is Killer Sudoku different from Kakuro?
Both use sums, but Killer Sudoku keeps all the Sudoku rules on a 9×9 grid, while Kakuro is a crossword-shaped grid with no rows-columns-boxes rule.
Can I print the same puzzles again?
Yes. The seed is printed in the footer of every page. Enter the same seed and level to rebuild the same puzzles and answers.
Is anything uploaded?
No. Puzzles, the PDF and the print view are created in your browser. Your last settings are remembered on this device only; see the privacy notice.
Prefer classic puzzles? The printable Sudoku maker makes 4×4, 6×6 and 9×9 sheets, and the large print Sudoku page has ready-made PDFs.