How to Play Killer Sudoku
Killer Sudoku is Sudoku with arithmetic bolted on. The grid is the usual nine by nine with the usual rules, but instead of givens you get cages: dotted outlines with a small number in the corner telling you what the squares inside add up to.
A cage never repeats a digit, and the normal Sudoku rules still apply everywhere. The sums are what get you started.
Play Killer SudokuHow to play Killer Sudoku
- Read the cage totals first and find the ones with only one combination. A two square cage summing to 3 can only be 1 and 2. One summing to 17 can only be 8 and 9.
- Write those pairs in as candidates, not as answers, until the order is settled by a row, column or box.
- Use the rule of 45. Every row, column and box adds to 45, so if cages cover a unit and leave one square over, that square is 45 minus the cage totals.
- Switch between sums and ordinary Sudoku logic. Each one keeps feeding the other.
- Finish the grid with 1 to 9 in every row, column and box, and every cage hitting its total.
Sums worth knowing
- Two squares: 3 is 1+2, 4 is 1+3, 16 is 7+9, 17 is 8+9.
- Three squares: 6 is 1+2+3, 7 is 1+2+4, 23 is 6+8+9, 24 is 7+8+9.
- Four squares: 10 is 1+2+3+4, 30 is 6+7+8+9.
- Any cage with a very low or very high total is a gift, because almost nothing fits.
Tips
No digit repeats inside a cage, which is why 9 plus 9 is never an answer for 18 in two squares. That single rule rules out most of the combinations people try.
A cage that sits entirely inside one box is worth more than one that straddles two, because everything it tells you lands in the same unit.
Frequently asked questions
What is the difference between Sudoku and Killer Sudoku?
Killer Sudoku usually starts with no given numbers at all. Instead you get cages with totals, and the sums are what let you work out the digits.
Can a digit repeat inside a cage?
No. A cage holds different digits, which cuts the number of possible combinations enormously.
What is the rule of 45?
Every row, column and box contains 1 to 9, so it totals 45. Comparing that with the cage totals covering it often hands you a single square for free.