How to Sudoku a Puzzle: A Zero-to-One Beginner Walkthrough

Step 1: Understand What You're Looking At

A standard Sudoku puzzle is a 9x9 grid divided into 81 smaller squares called cells. The grid is further divided into nine 3x3 regions, often outlined with a thicker border, called boxes or blocks. Your goal is to fill every empty cell (usually starting with 20-30 numbers given as 'givens') by following the one core rule: each row, column, and 3x3 box must contain all digits from 1 to 9, with no repeats.

Before you place a single number, take a moment to scan the puzzle. Look at the pattern of the givens. Notice that some rows, columns, and boxes have more starting numbers than others. This initial scan, not random guessing, is the first logical step in How to Play Sudoku.

Step 2: Find the Easiest Number – The Naked Single

Your first move should be to hunt for a Naked Single. This is a cell where, based on the numbers already placed in its row, column, and box, only one possible digit can go there. It's the most straightforward deduction in the game.

How to spot it: Look for the most crowded row, column, or box on the grid. A box with 7 or 8 givens is a great place to start. Find the single empty cell in that region. Check which numbers 1-9 are already present in that cell's row, column, and box. The one missing number is your Naked Single. Write it in confidently. For a deeper look at this fundamental move, see our guide on Naked Singles.

Step 3: Scan Rows and Columns for Hidden Singles

Once obvious Naked Singles are gone, your next tool is the Hidden Single. A digit is a Hidden Single for a cell if, within that cell's row, column, or box, it is the only possible cell left where that specific digit can be placed.

How to spot it: Pick a digit, say '5'. Scan one row from left to right. Ask: is there already a 5 in this row? If not, look at each empty cell in that row. For each empty cell, check if a 5 is blocked by a 5 in the column or box. If you find only one empty cell in the row where a 5 is *not* blocked, you've found a Hidden Single for digit 5. Repeat this scan for all digits across rows, columns, and boxes. Mastering this scan is a core skill, detailed in our Hidden Singles technique page.

Step 4: Start Using Pencil Marks (Candidate Notation)

When you can't immediately see a Naked or Hidden Single, it's time for pencil marks. These are small notes of possible digits (candidates) for each empty cell. Lightly write all digits 1-9 that are not ruled out by the row, column, and box.

Focus on one empty cell at a time. This systematic process often reveals numbers you missed. For instance, after filling in pencil marks for a row, you might notice that the digit '3' only appears as a candidate in one cell of that row – that's a Hidden Single revealed by notation.

• Keep pencil marks small and neat. Messy notes can lead to confusion.
• On paper, use a dot system in the corner of the cell. On apps, use the candidate notation feature.

Step 5: Apply Simple Eliminations

With pencil marks in place, you can start eliminating candidates. Look at a single 3x3 box. If you see that all candidate 7s in that box are confined to a single row or column, you can eliminate 7 as a candidate from the rest of that row or column outside the box. This is a basic form of intersection removal.

This elimination often creates new Naked or Hidden Singles. The process is cyclical: place a number, update pencil marks, look for eliminations, which leads to placing another number.

Step 6: Solve Your First Complete Region

Aim to completely fill one 3x3 box, row, or column. This gives you a solid foundation. Use the techniques above in combination. A box with 6 or 7 numbers is a good target. Use Naked/Hidden Singles to place numbers, then use those new numbers to eliminate candidates and find the next one in the same region.

Completing a region provides more information (more givens) for the surrounding rows and columns, making the next steps easier. This demonstrates the chain reaction of logic that defines Sudoku.