How to Play Sudoku: A Visual Beginner's Guide

Understanding the grid

A standard Sudoku grid is made of 81 cells. The thick lines divide it into nine smaller 3x3 boxes. A row, a column, and a box are each called a unit.

Each empty cell in the embedded player belongs to three units at once: one row, one column, and one box. A digit is legal only if it works in all three places.

When you tap a blank cell in the player, read it in this order: look across its row, look down its column, then look inside its 3x3 box. If a digit already appears in any of those places, that digit cannot go in the selected cell.

Three rules

1. Rows: every horizontal row must contain 1 through 9 exactly once.
2. Columns: every vertical column must contain 1 through 9 exactly once.
3. Boxes: every 3x3 box must contain 1 through 9 exactly once.

Standard Sudoku has no diagonal rule. Diagonals matter only in variants such as Diagonal Sudoku.

A properly constructed Sudoku has one unique solution. If a puzzle has more than one answer, it is not a proper standard Sudoku puzzle.

Make your first move

Start in the embedded player with the easiest unit you can find. Look for a row, column, or box that is almost complete. If a row already has eight different digits, the empty cell must take the one missing digit.

This is the safest beginner move: no guessing, no advanced pattern, just the missing number in one nearly complete unit.

If there is no unit with one blank, look for one with two or three blanks and compare those blanks against their crossing columns or rows. Often one blank cell is blocked by a digit that the other blank cell can still use. That is your next proven placement.

Scanning

Scanning means choosing one digit in the embedded player and checking where it can still fit in a row, column, or box. If a digit is already present in a row, no other cell in that row can take that digit. The same is true for columns and 3x3 boxes.

Work digit by digit. If a number can fit in only one cell inside a box, that placement is forced.

Naked singles

A naked single is a cell with only one possible candidate left. For a hypothetical example, suppose a row is missing 3 and 5, and one empty cell's column already contains 3. That cell must be 5 in a consistent puzzle. This illustrates the rule; it is not a claim about a particular cell in today's changing board.

In the embedded player, use the same test on any empty cell: check the row, check the column, check the box, and place a digit only when one candidate remains.

Pencil marks

Pencil marks are small candidate notes for empty cells. Use them when a puzzle stops giving you obvious placements. Write only the digits that do not already appear in the same row, column, or box.

Keep them tidy. When you place a number, remove that digit from the pencil marks in the same row, column, and box.

Guided practice in the embedded player

Use the embedded player above for the three beginner checks:

1. Last digit: find a row, column, or box with one empty cell and place the only missing digit.
2. Scanning: choose one digit and scan each row, column, and box to find where that digit can still fit.
3. Naked single: pick one empty cell and eliminate every digit already used in its row, column, or box.

A repeated digit immediately breaks a row, column, or box rule. A placement can also be wrong without an immediate repetition: later deductions may reveal the contradiction. Place a digit when you can explain why its alternatives are impossible.

For your first session, try a short practice period rather than aiming for a fast finish. Scan nearly complete units, choose one digit to follow, and check for naked singles. Add pencil marks where they help. Stop or take a break whenever you want; there is no required time limit.

What to do when stuck

1. Recheck rows, columns, and boxes with the fewest empty cells.
2. Scan one digit at a time, especially digits that already appear often.
3. Add pencil marks to a small area rather than the whole puzzle at once.
4. Look for naked singles and hidden singles before trying harder techniques.
5. Take a short break if every candidate starts to look the same.

An Expert label does not tell you which technique the next move needs. Difficulty varies by publisher. If your current methods stall, review candidates or study a worked lesson before choosing a value without a reason.

If you want a deeper checklist, use the companion guide on what to do when stuck on Sudoku. If the puzzle feels too hard, read Sudoku difficulty levels before moving from easy to medium.

Common beginner questions