Game guide
How to play Sudoku
In sudoku you fill a 9×9 grid with the numbers 1 to 9. The game ends when every row, every column and every 3×3 box has all nine numbers, with none repeated.
Updated on October 3, 2026
The rules in 3 lines
- 01
Fill the empty cells
Use the numbers 1 to 9. The numbers that come with the grid, in bold, are fixed.
- 02
No repeats in a group
Each row, each column and each 3×3 box has every number exactly once.
- 03
Correct grid, game over
When the last cell completes the solution, the clock stops and your time is saved.
How to play
On your phone
- Tap an empty cell to select it. Its row, column and box are highlighted.
- Tap a number on the keypad below the grid to write it.
- ⌫ erases the number in the selected cell.
- The “⋯” menu has New game, the level and How to play.
On a keyboard
- ← ↑ → ↓ move the selection.
- 1 to 9 write the number.
- Backspace, Delete or 0 erase.
- Esc closes the “⋯” menu.
Step-by-step example
To fit on screen, the example uses a 4×4 grid with the numbers 1 to 4 and 2×2 boxes. The logic is the same as in 9×9.
Before
After
If you write a number that already appears in the same row, column or box, it turns red. The game does not tell you whether a number is right: it only warns you when a number repeats.
Repeated
Beginner strategies
- Start with the fullest group. A row, column or box with 7 or 8 numbers leaves few options, sometimes just one.
- Look for the cell that takes only one number. Check its row, column and box together: the number missing from all three is the only option.
- Scan one number at a time. Pick 1, see where it already is, and work out which cell of each box can still hold it. Then do the same with 2, and so on.
- Use the highlight. When you select a cell with a number, cells with the same number light up, so it is easy to see where it is still missing.
Common mistakes
- Guessing. A guessed number feels like progress, but an early mistake spreads and only shows at the end. If you are not sure, leave the cell empty.
- Checking only the row. A cell has to fit its row, its column and its box at the same time.
- Carrying on with a red number. Red means repeated. Erase it before you continue.
- Doubting the fixed numbers. The bold numbers came with the grid and are correct. If something does not work, the mistake is in one of yours.
Levels and scoring
There are three levels: Easy, Medium and Hard. The harder the level, the fewer numbers the grid starts with. Every grid is generated on the spot and has exactly one solution. Your record is your best time on each level.
Frequently asked questions
Yes. The game only hands out grids with a single solution, so everything can be solved with logic, no guessing.
Some number does not match the solution, even if it is not repeated. Check the numbers you wrote last or guessed.
Yes. Your game is saved on this device and shows up as “Continue” in the games list.
There is no evidence that it does. Playing makes you faster and more confident at sudoku itself; it does not measure or change your IQ.
IQNorth games are a pastime with a challenge. Practice makes you better at this game; it does not raise your IQ or your memory, and nothing here is a consultation with a psychologist. The games are in the member area.
Guides for the other games
Word search · Sun and Moon · Colors · Sequence · 2048 · Challenges · Blocks · Pairs · One Line · Shape Fit · Sum Maze · Pipes
Was this helpful?
Thanks for letting us know.