Easy starts with 44 given numbers, Medium with 36 and Hard with 28. Every puzzle still has exactly one solution, whichever level you choose.
The number of given numbers depends on the level you pick.
Clues by level
- Easy: 44 given numbers, so 37 empty cells.
- Medium: 36 given numbers, so 45 empty cells.
- Hard: 28 given numbers, so 53 empty cells.
What the level means
Here, difficulty is set by how many numbers are given, not by which solving techniques a puzzle needs. Fewer clues mean more to work out and less to lean on. Every puzzle has exactly one solution.
Given numbers are fixed
You cannot change a given number. Only the empty cells take your entries and pencil notes.
For techniques that work at every level, read the Sudoku solving techniques guide. The full rules cover the rest.