How to play Sudoku
Sudoku is a logic puzzle played on a 9 × 9 grid. You never need to guess and you never need to do arithmetic: the numbers 1 to 9 are just nine different symbols. Every puzzle in Sudoku Arena has exactly one solution, and it can always be reached by reasoning alone.
The rules
The grid is divided into nine rows, nine columns and nine 3 × 3 boxes. Some cells already contain numbers (the "givens"). Your job is to fill every empty cell so that:
- each row contains the numbers 1 to 9 exactly once,
- each column contains the numbers 1 to 9 exactly once, and
- each box contains the numbers 1 to 9 exactly once.
That is the whole game. A number can only go in a cell if the same number is not already in that cell's row, column or box.
Your first moves
- Pick a number and scan. Choose a number that already appears many times, say 7. For each box that has no 7 yet, look along the rows and columns that pass through it. Lines that already contain a 7 rule out cells in that box. If only one cell is left, the 7 goes there.
- Look for crowded rows, columns and boxes. A row with seven or eight numbers filled in has only a few possibilities left. Check which numbers are missing and where each could go.
- Check a single cell. Pick an empty cell and list the numbers already in its row, column and box. If eight different numbers are ruled out, the ninth is the answer.
- Repeat. Every number you place gives you new information, so the puzzle gets easier as you go.
Playing in Sudoku Arena
- Entering numbers: tap a cell, then a number on the number pad. On a computer you can also type 1–9 and move with the arrow keys.
- Notes (pencil marks): switch on notes mode (or press N) to write small candidate numbers in a cell. Notes never count as mistakes, so use them freely on harder puzzles. When you place a number, matching notes in the same row, column and box are removed for you (you can turn this off in Settings).
- Mistakes: a wrong number is shown in red and counts as a mistake. After 3 mistakes the game is over, though you may be offered the chance to watch a short ad for one more try. Each mistake lowers your score.
- Hints: stuck? A hint fills in one cell and, where it can, explains the technique that proves it. You have 3 hints per game, and each one lowers your score a little.
- Pause: the clock stops while the game is paused or the app is in the background.
- Undo and erase: undo takes back your last entry or note; erase clears the selected cell.
The six difficulty levels
| Level | Numbers given | What it takes |
|---|---|---|
| Easy | 36–40 | Scanning and single candidates only. Ideal for learning. |
| Medium | 32–35 | Still singles, but you need to look harder for them. |
| Hard | 28–31 | Mostly singles, sometimes a pointing pair. |
| Expert | 26–30 | Pointing pairs, box/line reduction and naked pairs. |
| Master | 24–29 | Hidden pairs and triples; notes become essential. |
| Extreme | 20–26 | X-Wing, Swordfish and XY-Wing. No guessing needed. |
The techniques for the harder levels are explained step by step in our Sudoku strategy guide.
Tips for beginners
- Never guess. If you are not sure, keep looking: there is always a logical next step.
- Start with the numbers that appear most often. They have the fewest places left to go.
- Use notes once singles run out. Writing candidates down turns a hard search into a simple check.
- Take a break. A fresh look often reveals a move you missed. Your game is saved and the clock stops while paused.
- Play the Daily Challenge. Everyone gets the same puzzle each day, which makes it a great way to compare your times with friends.
How scores work
When you solve a puzzle you earn points for its difficulty, a time bonus for finishing quickly, and an extra 10% for a perfect solve with no mistakes and no hints. Mistakes and hints reduce the total. The details are on the scoring page.
Ready? Start an Easy puzzle or try today's Daily Challenge.