How to Play Sudoku

Since it first exploded onto the puzzling stage in 2004, Sudoku has become as much of a household name as Pictionary or the Sunday crossword. In part, the game has managed to succeed because of its simplicity: players are presented with a partly-empty grid and work to fill it with numbers. But it can be difficult, too. Make a single mistake and you’ll trigger a waterfall effect that’ll see you filling in dozens of incorrect answers. So how do you play Sudoku?

Rules of Sudoku

The Sudoku board is 9 x 9 squares or a total of 81 squares. Players work to fill these squares with numbers from 1-9, with the restrictions that the pre-filled numbers cannot be changed, and that there must be one of each integer in every row, column, and sub-box.

In order to solve the board, players need to use logic and strategy to figure out how many of each type of number is missing, and to identify which squares they need to be placed in.

Modified Sudoku Boards

Sudoku boards can vary in difficulty from simple to extremely difficult. Moreover, though there is a core, basic game, the game’s popularity means people have come up with plenty of their own variations.

For instance, mini sudoku is 6 x 6 squares; Alphabetical sudoku replaces numbers with letters and often expands the grid beyond 9 x 9 to squares of 12 x 12 or 16 x 16; and x-Sudoku requires that numbers 1 – 9 appear on both diagonals across the board, forming an ‘X,’ as well as in the rows and columns as is standard.

Best Ways to Approach the Board

If you’re new to the game, one of the hardest parts can be figuring out where to start. Here’s what we recommend:

  1. Solve by groups of numbers, not by sections of the board.

One of the most common mistakes by Sudoku novices is to attack the board in sections. While it may seem intuitive to move square-by-square or row-by-row, in fact, at the beginning of the game, you usually don’t have enough information to enter any numbers. If you go for this strategy, you’ll likely find yourself stuck before you even get started. Instead, move number-by-number across the board. For instance, start with the number one. Look at all the 1s on the board, and try to identify which squares, rows, or columns are missing 1s. Then see if you can plug in any of those missing numbers.

  1. Start with the number that you see most on the board.

One strategy for picking where to start is starting with the first number, 1. But another way to go about things is to pick the number that appears the most on the board. If you can find a number that appears 8 times, for instance, you’ll know you definitely have the information to plug in the number into its required ninth spot.

  1. If you’ve narrowed down a square to two or three options, make a note of it.

You can do this by making a small note in the top corner of each square. While it may seem like you can easily find this information again later, making a note can help you narrow down the location of other numbers. For instance, if you know the numbers 2 and 3 must appear in one of two squares, write it down so that later you know not to plug an 8 into those spots.

  1. Once you’ve gone through all the numbers once, circle back to the first number. 

Once you’ve gone through each number, circle back to the number you started with. Though this may seem redundant, in fact, the extra numbers you’ve been able to fill in will narrow down your options. While you might not have been able to place any 1s during your first attempt, for instance, you may find the board has been filled out and your options have narrowed, meaning you can place numbers now.

  1. If you get stuck, try to retrace your steps.

It happens even to the best of us: eventually, you’ll find yourself stuck. Maybe you’ve made a mistake at some point, and it’s led you to gridlock, or maybe you just don’t know where to go next. When you find yourself in this position, don’t panic. Instead, try to backtrack and retrace the steps you’ve made so far. By checking your answers, you might find something you overlooked or an error you made. Fixing that small detail may be all you need to do to move forward.

  1. Remember, every Sudoku square can – and must – be solved without guessing!

Another novice mistake is to assume that guessing has a place in Sudoku. It does not. Even if you think there is no information to help you decide what square to put a number in, don’t just randomly place it. You might get lucky, and find you’re right, or you might be wrong, and make a much bigger headache for yourself down the line. Instead, try to be patient and measured, and search for moves you can be sure of, instead of ones you find doubtful in any way.

Our Other Sudoku Resources

If this blog post has you determined to try your hand at Sudoku, you’re in luck! TheWordFinder has plenty of Sudoku resources for your next game. First, be sure to check out our Play Sudoku game, which will allow you to play a digitized version of Sudoku. This game is perfect for those still getting introduced to Sudoku, as you can wipe answers or restart as often as you’d like without destroying your workbook with an eraser. Or, in the future, if you’re stuck on a game, try our Sudoku Solver, which will allow you to instantly solve any Sudoku puzzle.