Free Printable Hard Killer Sudoku
A freshly generated hard killer sudoku — larger cages, deeper logical chains, full A4 sheet.
Killer SudokuFree printable hard killer sudoku puzzles — the cage combinations start working harder than the digit logic. Killer rules: classic 9×9 sudoku (row, column, 3×3 box uniqueness) plus dashed-outlined cages, each with a target sum and unique-digits constraint. The grid ships empty; cages and their sums are the puzzle.
Hard killer leans on larger cages — three- and four-cell groups are common, sometimes a five-cell cage spans a corner. Cage-combination enumeration is now mandatory: a 4-cell cage summing to 11 has only a few valid digit sets (1+2+3+5 among them), and listing each set is often the move that breaks the puzzle open. The 45 rule applies on multiple axes simultaneously — find the innie (a single cell completing a row that's otherwise fully caged) and the outie (a single cell from a partial cage poking into a row), and the puzzle yields fast.
Plan on forty to seventy minutes with pencil marks. Print full-page so the cage outlines stay crisp. Free, no account, no watermark, freshly generated every load.
Frequently asked questions
Quick answers about printing sudoku from Sudoku247Online.
- What is killer sudoku and how does it differ from classic?
- Killer sudoku uses the same 9×9 grid as classic, but the puzzle ships empty. Cells are grouped into outlined regions called cages, and each cage carries a target sum. Standard row/column/box rules still apply, plus digits inside a cage must be unique and add up to the cage's sum.
- Why is the printed grid completely empty?
- Killer puzzles have no starting digits — the cages and sums are the puzzle. Everything you need to solve is right there: the cage outlines and the small sum number in the corner of each cage's anchor cell.
- What do the small numbers in the cells mean?
- Each small number in the top-left corner of a cell is the sum target for the cage that cell anchors. Cage boundaries are drawn as dashed lines. Every cell belongs to exactly one cage.
- How long does a killer sudoku take to solve?
- Easy killer takes 15–25 minutes, medium 25–40, hard 40–70, expert often over an hour. Cage-sum combinations open up most of the early moves; classic sudoku scanning closes them.
- What techniques are essential for killer sudoku?
- Cage-sum arithmetic is the killer-specific layer: the '45 rule' (every row/column/box sums to 45), cage combinations (e.g. a 3-cell cage summing to 6 must be 1-2-3), and innies/outies. Standard sudoku techniques (naked singles, hidden singles, pointing pairs) carry over for the placement step.
- Are the solutions printed with the puzzle?
- Not on the standalone killer printables yet — solving online at /killer-sudoku reveals the solution on completion. A 'Print with solutions' option for killer is on the roadmap.