How to Solve Sudoku Step by Step

What Is Sudoku and How Does the Puzzle Work?

Sudoku can look confusing at first glance. But once you understand the structure, the puzzle becomes much more approachable — and genuinely satisfying to solve.

The 9×9 Grid Explained

Every sudoku puzzle is played on a 9×9 grid: 81 cells arranged in nine rows and nine columns. Some cells arrive pre-filled with numbers called givens or clues. Your job is to fill every remaining empty cell with a digit from 1 to 9. For a full breakdown of the grid zones, see the Sudoku Rules page.

Rows, Columns, and Boxes

The grid contains three types of zones. A row runs horizontally, a column runs vertically, and a box is one of the nine 3×3 sections that partition the grid into equal blocks. Every row, column, and box must contain the digits 1 through 9 with no repeats.

The One Rule That Governs Every Puzzle

Sudoku involves no arithmetic. You are simply placing nine unique digits so that no digit appears twice in the same row, column, or box. That single rule underpins every solve. Every logic technique you will ever use is just a different way of applying it.

Step-by-Step: How to Solve Sudoku for Beginners

Follow this sequence each time you sit down with a new puzzle.

Step 1: Scan Rows and Columns for Missing Numbers

Begin by scanning each row and each column to identify which digits are already placed. If a row contains 1, 3, 4, 5, 6, 7, 8, and 9, then 2 is the only missing digit and belongs in the one remaining empty cell. Always claim these easy wins before moving on.

Step 2: Focus on Boxes With the Most Filled Cells

A box containing seven or eight digits leaves almost no room for ambiguity. Tackle the most complete boxes first — the fewer empty cells, the easier it is to determine what each one must hold.

Step 3: Use the Process of Elimination

Elimination means ruling out digits that cannot legally occupy a particular cell. If the digit 7 already appears in that cell's row, column, and box, it cannot be placed there. Work through options systematically rather than guessing. This is the same principle behind naked singles — the most fundamental technique in sudoku.

Step 4: Write Candidate Numbers in Empty Cells

When a cell cannot be solved immediately, jot small pencil marks — called candidates — inside it to list every digit that could legally go there. If only 4 and 8 remain possible, write both. These notes become the foundation of your logic in later steps and eliminate the most common source of beginner errors. (More on that in the companion article: Common Sudoku Mistakes Beginners Make.)

Step 5: Apply Logic to Confirm Placements

With candidates written in, look for any cell where only one candidate survives. That digit is confirmed — place it. Then remove it from the candidate lists of every other cell sharing the same row, column, or box, and repeat. This is the core loop of sudoku solving.

Essential Techniques Every Beginner Should Learn

Two core techniques will carry you through most easy puzzles and many medium ones without guessing. Both are covered in depth in the Learn hub.

Single Candidate Method (Naked Singles)

This applies when elimination leaves just one possible digit in a cell. If a cell's row already contains 1, 2, 3, 4, 5, 6, 7, and 9, then 8 is the only candidate — place it immediately. Each confirmed placement then triggers further eliminations across connected rows, columns, and boxes. See the full guide: Naked Singles.

Single Position Method (Hidden Singles)

Instead of focusing on a cell, this technique focuses on a digit. Scan a box and ask: how many cells could legally hold the digit 5? If only one cell in that box can accommodate a 5 without conflicting with its row or column, place it there. This is called a hidden single and often clears candidates from entire rows and columns in a single step.

Common Mistakes to Avoid

Breaking these two habits early will prevent the vast majority of errors.

Guessing Instead of Using Logic

Guessing is the most damaging beginner habit. A digit placed without logical proof can corrupt the grid several moves later in ways that are difficult to trace. Every placement should follow a rule you can articulate. If you cannot justify a digit, leave the cell until you can. For a full breakdown of what goes wrong and how to fix it, see Common Sudoku Mistakes Beginners Make.

Forgetting to Check All Three Zones

Elimination only works when you check the row, the column, and the box together. Skipping one zone produces incomplete candidate lists and incorrect placements. Run all three checks every time you assess a cell — make it automatic.

What to Do When You Get Stuck

Getting stuck is a normal part of learning. Before assuming a puzzle requires guessing, take these steps.

First, return to pencil marks. If you have not written candidates into every unsolved cell, do that now. Incomplete candidate lists are the most common reason progress stalls. Second, switch zones — if you have been focused on one box, move to a row or column that intersects it. Third, look for the single position pattern across the whole grid rather than box by box.

If none of these produce a move, revisit your earliest placements. A single incorrect digit entered early can block progress many steps later. The Sudoku Tips page includes a full stuck playbook and a 7-day practice plan to build these habits.

Practice: Try a Free Sudoku Puzzle Now

The fastest way to learn is to open a real puzzle and work through each technique directly. Try today's Daily Sudoku — one Medium puzzle per day, the same grid for everyone. Or print a free sudoku puzzle in Easy or Medium to practise at your own pace with a real pencil in hand.

Frequently Asked Questions