Is Killer Sudoku harder than Sudoku? It depends how you think

Killer Sudoku isn't simply harder than Sudoku. It's different, and which one you find harder depends on how you think. People who dislike arithmetic often struggle with Killer. People who got stuck in ordinary Sudoku because a puzzle gave them too few clues sometimes find Killer easier, because the cages hand them something to work with.

What changes

Killer Sudoku keeps the Sudoku rules: each row, column and box holds the digits 1 to 9 once. What it adds is cages, small groups of cells outlined on the grid, each with a total in the corner. The digits in a cage must add up to that total, and no digit repeats inside a cage.

The big difference is what you're given at the start. A classic Sudoku gives you a scatter of digits. None of our Killer Sudoku books give you any. The cages carry all the information.

The skills

Classic Sudoku is mostly scanning and elimination. You look along rows and columns and ask where a digit can still go.

Killer asks something else: which digits can make this total? A two-cell cage totalling 3 can only hold 1 and 2. A two-cell cage totalling 17 can only hold 8 and 9. A three-cell cage totalling 6 must be 1, 2 and 3. Those little facts are the foothold, and once you have a few of them the ordinary Sudoku logic takes over.

Why the difficulty labels don't carry over

An Easy Killer Sudoku is not an Easy Sudoku. The key to difficulty in Killer is the absence of given digits, so you have to find cages with only a few possible combinations to get started. That also gives us a way to grade the puzzles beyond the usual Sudoku levels: the harder the puzzle, the fewer easy cages there are to start from.

So if you find Hard Sudoku comfortable, don't assume you'll breeze through a Hard Killer. Treat the level as a fresh scale.

Where to start

• You do Sudoku in minutes and like arithmetic: go straight to one of the harder volumes. 1000+ Killer Sudoku Variants mixes 8x8, 9x9, 10x10 and 12x12 grids, plus Killer X and Killer Windoku.
• You do Sudoku in minutes and dislike arithmetic: start at Novice and give the sums a week before you decide.
• You're newer to Sudoku: build your Sudoku first. Killer is more fun when the basics are automatic.
• You want to take it with you: 240 Pocket Killer Sudoku goes in a bag, and 157 Large Print Killer Sudoku makes the cage totals easy to read.

Whichever you pick, try one Novice puzzle before you decide. You'll know within a page or two whether the sums suit you.