WorldPuzzle

Hard Sudoku

For players who want a real mental workout

Hard Sudoku strips the grid down to around 28 clues and demands serious logic. Expect to use pencil marks, naked pairs, hidden singles and elimination chains. If Easy and Medium feel like a warm-up, this is the workout.

How to Play Sudoku Hard

  1. Rules are the same as classic Sudoku: 1-9 exactly once per row, column and box.
  2. Hard grids start with roughly 28 given numbers.
  3. Pencil marks are essential — fill candidates for every empty cell.
  4. Look for pairs, triples and locked candidates to eliminate options.
  5. Complete the grid to win.

Tips & Strategies

Master the "naked pair" technique: if two cells in a row share the same two candidates, those numbers can be removed from all other cells in the row. Combine pencil marks with cross-hatching and you will beat even expert-level grids.

Frequently Asked Questions

What techniques do I need for hard Sudoku?

Pencil marking, naked pairs, hidden pairs, and locked candidates are the most important tools at this level.

How long does hard Sudoku take?

Most experienced players solve hard grids in 20-40 minutes; beginners may need longer or can practice on Medium first.

Can I undo mistakes?

Yes — use the Undo button or erase your last entry at any time.