Sudoku looks like a math puzzle, but it isn’t. It’s a logic puzzle with a small rule set. Once you understand the rules clearly, Sudoku becomes far less intimidating.
Sudoku is a **9×9 grid** divided into **nine 3×3 boxes**. Some numbers are already filled in (called *givens*). You fill the empty cells using digits 1–9 so the final grid follows the rules.
### Rule 1: No repeats in any row
Each row must contain 1–9 exactly once.
### Rule 2: No repeats in any column
Each column must contain 1–9 exactly once.
### Rule 3: No repeats in any 3×3 box
Each 3×3 box must contain 1–9 exactly once.
Every placement must satisfy **row + column + box** simultaneously.
Think of Sudoku as 9 rows, 9 columns, and 9 boxes.
Every cell belongs to exactly one of each. When you place a number, check:
If “yes” to any, it’s invalid.
Candidates are numbers that could legally fit in an empty cell.
To find candidates:
1) Remove digits already in the row
2) Remove digits already in the column
3) Remove digits already in the box
Whatever remains is legal. Sudoku is often about eliminating impossibilities.
Givens are fixed anchors. A proper puzzle is designed so the givens lead to the solution logically.
No calculations. A 9 isn’t “bigger” than a 1 here—digits are just symbols that must not repeat within the same unit.
Easy puzzles allow simple deductions (missing digits, basic elimination). Hard puzzles require more complex candidate patterns, but the rules never change.
1) Each row contains 1–9 once
2) Each column contains 1–9 once
3) Each 3×3 box contains 1–9 once
**Is Sudoku always 9×9?** Most common is 9×9, but variants exist.
**Do I need to guess?** Easy puzzles shouldn’t require guessing.
**What do beginners miss most?** The 3×3 box constraint.
Master the three rules and Sudoku becomes a structured logic game. From here, the next step is applying beginner-friendly strategies efficiently.
Imagine a blank cell in the top-left box. The row already contains 1, 4, 7, and 9. The column already contains 2 and 8. The box already contains 3 and 6. When you combine those three checks, the only digit left is 5. That is a legal placement because it satisfies row, column, and box at the same time.
This example is the basic shape of almost every Sudoku decision. You are not trying to guess what looks right. You are collecting constraints until only one option remains.
Use the same order every time you enter a number: row first, column second, box third. A fixed order keeps you from skipping the box check when a row looks obvious. If a number survives all three checks, it may be a valid candidate. If it is the only candidate, it can be placed.
For your first few puzzles, say the checks out loud or write them briefly in notes. It may feel slow, but it builds the habit that prevents most beginner errors later.
After the rules feel natural, move to a step-by-step solving routine. The next skill is not another rule; it is learning where to look first so you do not scan the whole board randomly.