Free Sudoku online: easy, medium, hard and expert
Play classic 9×9 sudoku with a daily puzzle at every level, or generate unlimited new puzzles. Every puzzle has exactly one solution.
How to play sudoku
Fill the 9×9 grid so that every row, every column and every 3×3 box contains the numbers 1 to 9 exactly once. Tap a square, then tap a number (or use the arrow and number keys on a keyboard). Wrong numbers show in red, so you can learn as you go.
Our four levels
| Level | Starting numbers | What you need |
|---|---|---|
| Easy | 40 | Scanning and single candidates |
| Medium | 32 | Plus hidden singles in rows and columns |
| Hard | 27 | Plus pairs and pencil marks |
| Expert | 24 | Plus box-line reduction and careful notes |
Every puzzle is generated and then checked by a solver to make sure it has exactly one solution. You never need to guess.
Solving techniques, from easy to hard
1. Scanning (cross-hatching)
Pick a number, say 5. Look at each box that doesn't have a 5 yet. Cross out every row and column in that box that already has a 5 somewhere else. If only one empty square is left, the 5 goes there. This alone solves most easy puzzles.
2. Single candidate (naked single)
Look at one empty square. List the numbers already in its row, column and box. If eight different numbers are there, the ninth is the answer.
3. Hidden single
Look at one row. If a number, say 3, can only go in one square of that row (because every other empty square already sees a 3), it must go there, even if that square has other possibilities too.
4. Naked pairs
If two squares in the same row can each only be 4 or 7, then 4 and 7 must go in those two squares. You can remove 4 and 7 as options from every other square in that row.
5. Box-line reduction (pointing)
If, inside one box, all the possible spots for a number lie in the same row, then that number must be in that row inside that box. So you can remove it from the rest of the row outside the box. Expert puzzles often need this step.
Tips
- Always scan for all nine numbers before using pencil marks. It's faster.
- Start with the numbers that already appear most often in the grid.
- If you get stuck, look for the row, column or box with the fewest empty squares.
Each level has its own daily puzzle, and you can replay older daily puzzles from the puzzle archive. For more, read our guide to sudoku techniques with examples.
Frequently asked questions
Do all puzzles have one solution?
Yes. Every puzzle is checked so that it has exactly one valid solution.
Can I use the keyboard?
Yes. Use the arrow keys to move and number keys to fill squares. Backspace erases.
Is it free?
Yes, every level and every puzzle is free with no sign-up.
How many numbers does each level start with?
Easy starts with 40 numbers, medium 32, hard 27 and expert 24.
Do I need to guess?
No. Every puzzle has exactly one solution and can be solved by logic.
Can I replay an old daily puzzle?
Yes. Pick any earlier day from the puzzle archive.