Sudoku takes a minute to learn. You need no maths and no special knowledge, just a little patience and the habit of asking “where can this digit go?”
The rules
A sudoku is a 9×9 grid divided into nine 3×3 boxes. Some cells already hold a digit; these are the givens, and they never change.
Fill every empty cell so that:
- Each row contains the digits 1 to 9 exactly once.
- Each column contains the digits 1 to 9 exactly once.
- Each 3×3 box contains the digits 1 to 9 exactly once.
That’s all. A well-made puzzle has exactly one solution, and you can reach it by logic alone. If you find yourself guessing, there’s a step you haven’t spotted yet.
Words you’ll see
| Word | Meaning |
|---|---|
| Cell | One square of the grid. There are 81. |
| House | Any row, column or box. Every house holds 1 to 9 once. |
| Given | A digit printed at the start. |
| Candidate | A digit that could still go in an empty cell without breaking a rule. |
| Peer | Any cell that shares a row, column or box with another cell. |
Your first puzzle, step by step
1. Scan for one digit at a time
Pick a digit, say 1. For each box, look at the rows and columns that already contain a 1 and mentally cross them out. If only one cell in the box is left for 1, write it in. Then move on to 2, 3 and so on up to 9.
This is called a Hidden Single, and it carries most beginner puzzles a long way.
2. Check crowded cells
When a row, column or box is nearly full, look at its empty cells one by one. For each, cross out every digit already among its peers. If only one candidate survives, that’s the answer. This is a Naked Single.
3. Repeat
Every digit you place blocks more cells for its peers, which opens up new singles. Keep alternating between scanning digits and checking crowded cells. On an easy puzzle, these two moves are all you’ll need.
4. Use notes when you get stuck
If neither move finds anything, start pencilling candidates into the empty cells. Notes turn “I can’t see anything” into a list you can reason about, and they’re the gateway to the next techniques. Learn Sudoku: A Clear Path from Easy to Expert takes you through them in order.
Common beginner mistakes
- Guessing. A guess that happens to be right teaches you nothing, and a wrong one can wreck the grid twenty moves later. If you’re stuck, look again; there is always a logical step.
- Forgetting the boxes. Rows and columns are easy to see; boxes are easy to forget. Check all three every time.
- Stale notes. If you place a digit and don’t remove it from its peers’ notes, the notes start lying to you. (One Sudoku clears them for you automatically.)
Where to go next
Start with Easy puzzles until you can finish one in about five minutes, then move to Medium, where Hidden Singles become essential. When you’re ready for more, these guides go one step at a time:
- Sudoku Tips for Beginners
- Naked Pairs, the first technique that removes candidates instead of placing digits
- How Sudoku Difficulty Is Graded
Once classic sudoku feels comfortable, Killer Sudoku adds cages and sums on top of the same rules.
