How to Solve Sudoku: Complete Beginner Guide

Everything you need to know to fill in your first grid.

The Three Rules

Sudoku has exactly three rules. If you remember these, you can solve any puzzle:

1. Each row must contain the digits 1 through 9 with no repeats.
2. Each column must contain the digits 1 through 9 with no repeats.
3. Each 3x3 box must contain the digits 1 through 9 with no repeats.

That is it. No math. No adding. No multiplication. You just place digits so none of them repeat in any row, column, or box.

The Grid Layout

A standard Sudoku grid has 81 cells arranged in 9 rows and 9 columns. The grid is also divided into nine 3x3 boxes (sometimes called blocks or regions). When you start a puzzle, some cells already have numbers in them. These are called givens. The more givens a puzzle has, the easier it is. Easy puzzles might have 36 to 45 givens. Expert puzzles can have as few as 17.

Step 1: Scan the Grid

Start by looking at the grid as a whole. Find rows, columns, or boxes that already have several numbers filled in. These are the easiest places to make progress because fewer options remain.

For example, if a row already has 1, 2, 3, 5, 6, 7, and 9, the only missing number is 4 and 8. Now look at the two empty cells in that row and check their columns and boxes. One of the two cells will already see a 4 or an 8, which tells you exactly where each goes.

Step 2: Use Elimination

Pick an empty cell. Look at its row, column, and box. Cross off every number that already appears in any of those three groups. Whatever is left is a candidate for that cell. If only one number is left, fill it in.

This technique is called naked singles. It is the foundation of all Sudoku solving. Most easy puzzles can be solved with naked singles alone.

Step 3: Look for Hidden Singles

A hidden single is a number that can only go in one cell within a row, column, or box, even though that cell might have other candidates. For example, if you are looking at a 3x3 box and the number 7 can only go in one of the empty cells (because all other empty cells in that box already see a 7 in their row or column), then 7 must go there.

Step 4: Write Pencil Marks

When puzzles get harder, you will not be able to solve cells one at a time. Instead, write small candidate numbers (pencil marks) in each empty cell. This gives you a map of possibilities. As you fill in cells, erase candidates from neighboring cells. Pencil marks make advanced techniques possible.

Step 5: Practice

Start with easy puzzles. Solve ten or twenty before moving to medium. Do not skip ahead to hard puzzles until you can solve mediums in under 15 minutes. Every level builds on the one before it.

Our puzzle books start at easy and go all the way to expert. The free app has puzzles at every level too, with built-in pencil marks and hints if you get stuck.

Common Mistakes

• Guessing. Sudoku is logic, not luck. If you are guessing, you missed something. Back up and look again.
• Forgetting a box. Always check all three constraints: row, column, and box.
• Skipping pencil marks. You need them for anything harder than easy puzzles.
• Not scanning first. A quick scan often reveals several easy fills before you have to think hard.

Ready to Start?

Grab a free printable puzzle, open the app, or pick up Volume 1 (Easy) and work through your first 200 grids. You will be solving hard puzzles before you know it.