How to Play Sudoku

Guide Note: Sudoku is the little game of logic that has captured the nation's heart. But if the array of numbers and squares looks like Greek to you, there's no reason to be intimidated—this page will show you how simple it is to learn How to Play Sudoku.

Table of Contents:

Introduction

(Creative Commons photo by Eduardo Mueses)
(Creative Commons photo by Eduardo Mueses)
  • If you've opened up a newspaper in the past year, you've probably seen a strange looking puzzle game that resembles a crossword with numbers. This is Sudoku, a simple concept that has quickly become one of the most popular games in the country (if not the world).
  • If you're not a math whiz, don't let the numbers intimidate you. In fact, you don't need to know any math at all in order to enjoy Sudoku, as it is simply a game of logic. If you can count to nine, you can play! This page will give you the rundown on the rules, plus some strategies to get you started on this addictive puzzle game.

Sudoku Rules

  • Sudoku is played on a grid of 81 squares that looks like this:


  • You'll notice that it consists of 9 larger boxes, each containing 9 squares within their borders. For the purposes of instruction, we will number each large box 1-9 as labeled above. In Sudoku, each box, row and column will contain one of each digit 1-9.


  • But in an actual game they will not be laid out so simply as in the illustration above. Rather, they are jumbled in a random order, with most of them removed from the equation (leaving a select few digits that you will use as clues). The end goal is to take an unsolved Sudoku puzzle and fill in the blanks so that every column, row, and box contains all nine digits with no repeating numbers.
  • The following example is from a puzzle found on Websudoku.com. The one on the left is what the completed puzzle looks like, except that parts of it are highlighted in color, in order to illustrate the concept. Among the jumble of numbers you can see one row (blue), column (red), and box (yellow) containing the numbers 1-9. Look more closely and you'll see that each and every row/column/box meets this qualification. The puzzle on the right is what it looks like unsolved. Some numbers are given to you to work from, but most of it is blank. There is only one solution to any given Sudoku puzzle. A simple concept, right? But how do you get started?


DID YOU KNOW: On a standard 9x9 Sudoku grid there are 6,670,903,752,021,072,936,960 possible original puzzle layouts?

Getting Started

  • Sudoku is a process of elimination. Therefore, the idea is to find places in the puzzle in which certain numbers must be. One way to do this is by looking for numbers in the grid that appear multiple times. For example, if we look at the unsolved puzzle from the previous section, we see that there are 7s in boxes 4 and 6: in the top row of 4 and the bottom row of 6. This means that box 5 must have a 7 in its own middle row. Since there is only one open spot between the 6 and the 3, we know for a fact that a 7 belongs there (Example A).
  • Similarly, there are multiple 8s in the puzzle. Looking down the center at boxes 2, 5, and 8, we see that the number 8 must be in the right-hand column of box 8, where there are two spaces available. But you'll also notice that there is an 8 in the very bottom row of box 9, eliminating all but one spot in box 8 (Example B).


  • Sometimes you'll have to use your noggin a bit more to find a solution. Now that we've filled the 8 in, the only remaining digits in that box are 1, 5, and 6. We know those digits have to be in the bottom row, but we don't know in exactly what order. However, we can use that knowledge to place the 6 in box 7. Knowing that a 6 must be in the bottom row eliminates two spaces in box 7. Combining that with the placement of 6s in boxes 4 and 9, we can establish exactly where the 6 must be in box 7! (See illustration below.)


  • Are you still following? Good! As you fill in each number, you eliminate more and more possibilities, making the puzzle easier and easier to solve—just like letters in a crossword puzzle. This is one of the basic strategies for solving Sudoku, but you may find yourself hitting the wall at some point, specifically in a case when there are no guaranteed digits to be found. Luckily, there are other methods for resolving the Sudoku madness.

Strategies

(Creative Commons photo by Tim Psych)
(Creative Commons photo by Tim Psych)
  • More advanced Sudoku puzzles will be hard to solve by sticking to a single method. Here are some things to try if you get stuck.

Change What You're Looking At

  • Think you're stuck? Think again. Many times when you think you've hit the wall, there are actually solutions right in front of you that you've simply overlooked.
  1. If you're feeling overwhelmed, only look at rows for a while. Or try only looking at boxes or columns. This can help get your mind focused without meandering!
  2. Change your row/column/box perspective. Often you'll find yourself agonizing over a particular space in a column without realizing that you already have 8 or 9 spaces of the row filled in.
  3. Move to a new area of the puzzle. If you feel like you can't go any further in the lower right hand corner, start looking for solutions in the upper left. A breakthrough in one area of the grid can lead to solutions in others.

Grab a Pencil

  • You're probably already using one if you're not playing online, but you can complete any Sudoku puzzle with a few erasable notes.
  1. If you've narrowed down a spot to only a couple digits, write them both down for a reference. Then you won't have to memorize all the possibilities and it will help give you a visual reference while working the puzzle out.
  2. You can solve just about any Sudoku by writing all nine digits in each blank space (you can also use dots as explained in the Sudoku Wikipedia article).
    • When a number is eliminated from a given space, erase it. When only one number remains, that is the answer.
    • If a number appears as a possibility in only one space of any box, row, or column (even if it's not the final number remaining in said space), it is the answer.
    • If any box/row/column contains two spaces with matching pairs of numbers (like in this Howstuffworks example in which they show two spaces in the row containing only the possibilities of 5 and 6), those two numbers will definitely be in those spaces, although you don't know in which order. Therefore, you can eliminate the possibility of those numbers from any other space in that box/row/column.
    • Using this method is a surefire way to complete a puzzle unless it is designed to be impossible to solve without guessing.
  3. If you don't feel like writing all those digits, just focus on one area.

Play Daily!

  • Just like with any acquired skill, you'll get better and better at Sudoku if you just practice. There are enough newspapers and websites that print a daily puzzle, so you can solve one every day and work your way up to higher levels of difficulty!

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Resources for How to Play Sudoku

Online Sudoku

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