How to use the calculator
- Set Cells to the number of squares in the cage and Total to the number in its corner.
- Read the bar above the list. Always in shows the digits every combination shares, so the cage must contain them. Never shows the digits no combination uses.
- Tap a digit once if you already know the cage contains it, and twice if it can't. Combinations that no longer fit turn dim, and the bar updates.
- Tap a combination to strike it out once you have ruled it out on the grid.
- Playing a 6×6 killer? Switch to 6×6 and the digits run from 1 to 6.
The 45 rule
The digits 1 to 9 add up to 45, and every row, column and box contains each of them once. So if the cages lying entirely inside a row add up to 38 and one cell of that row is left over, that cell must be 7.
It works for more than one leftover cell too: their total is 45 minus the cages around them, which gives you a new cage to look up. Solvers call these cells innies. Cells that belong to a cage poking out of the house are outies, and the same subtraction tells you what they add up to. The panel above does the arithmetic for cages that sit entirely inside one row, column or box.
Cages with only one combination
These totals can only be made one way. Spot them early: they give you digits for free. An 8-cell cage is missing exactly one digit, the one equal to 45 minus its total.
2 cells
- 3
- 1 2
- 4
- 1 3
- 16
- 7 9
- 17
- 8 9
3 cells
- 6
- 1 2 3
- 7
- 1 2 4
- 23
- 6 8 9
- 24
- 7 8 9
4 cells
- 10
- 1 2 3 4
- 11
- 1 2 3 5
- 29
- 5 7 8 9
- 30
- 6 7 8 9
5 cells
- 15
- 1 2 3 4 5
- 16
- 1 2 3 4 6
- 34
- 4 6 7 8 9
- 35
- 5 6 7 8 9
6 cells
- 21
- 1 2 3 4 5 6
- 22
- 1 2 3 4 5 7
- 38
- 3 5 6 7 8 9
- 39
- 4 5 6 7 8 9
7 cells
- 28
- 1 2 3 4 5 6 7
- 29
- 1 2 3 4 5 6 8
- 41
- 2 4 5 6 7 8 9
- 42
- 3 4 5 6 7 8 9
Every other total has more than one combination. See them all on the killer sudoku combinations chart, or let the killer sudoku solver work through a whole grid with you.
Frequently asked questions
What is killer sudoku?
Killer sudoku keeps the normal sudoku rules: every row, column and 3×3 box holds the digits 1 to 9 once. On top of that the grid is split into cages, each marked with a total. The digits in a cage add up to that total, and no digit repeats inside a cage. Most killer sudokus give no starting digits, so the totals are all you have.
Can a digit appear twice in the same cage?
No. In standard killer sudoku the digits in a cage are all different, even when the cage spreads across two boxes. That rule is what makes the combinations useful: 2 cells totalling 4 can only be 1 and 3, never 2 and 2.
How many cage combinations are there?
With the digits 1 to 9 there are 502 different combinations for cages of 2 to 9 cells. The full chart, grouped by cage size and total, is on the killer sudoku combinations page.
What does "always in" mean?
It lists the digits that appear in every combination still on the table, so the cage must contain them somewhere. For 3 cells totalling 23 the only combination is 6, 8 and 9, so all three are always in. "Never" is the opposite: digits that no remaining combination uses.
Does it work for kakuro?
Yes. A kakuro run follows the same rule as a killer cage: different digits from 1 to 9 that add up to the clue. Set Cells to the length of the run and Total to its clue.
Can it solve a whole killer sudoku?
Yes, on the solver page. Draw the cages, type their totals, and ask for the next step: it explains why a digit goes where it does. You can also reveal the full solution.
Do I need to sign up, and is anything sent anywhere?
No sign-up. Everything runs in your browser; the numbers you enter are not sent to a server.