How to Play Sudoku: A Complete Beginner's Guide

Sudoku is a number-placement puzzle that, despite the digits, has nothing to do with arithmetic. You won’t add, multiply, or calculate anything. The numbers are just labels; you could play sudoku with nine letters, nine emojis, or nine tiny pictures of samurai. The puzzle is pure logic, and that’s why it became one of the most-played pastimes on earth.

This guide is for someone who has never solved a sudoku before, or who has tried once, gotten stuck, and quietly closed the newspaper. By the end, you’ll know the rules, understand the structure of the board, and have a method for solving your first puzzle without guessing. We’ll go slowly. There’s no math. There’s no trick.

The board

A standard sudoku board is a 9×9 grid: 81 cells in total. The grid is divided into three structural units, and every rule of sudoku flows from these three units:

• Rows: nine horizontal lines of nine cells each.
• Columns: nine vertical lines of nine cells each.
• Boxes: nine 3×3 sub-grids, separated by the thicker grid lines you’ll see on any sudoku board.

Each cell sits at the intersection of one row, one column, and one box. That single fact is the key to everything. When you place a number in a cell, it isn’t just sitting in a row. It is simultaneously locking that number out of a row, a column, and a box. Three constraints at once. Sudoku is the sustained consequence of that triple constraint.

The one rule

The puzzle has a single rule, stated three ways:

Every row, every column, and every 3×3 box must contain the digits 1 through 9 exactly once.

That’s it. There is no other rule in classic sudoku. No diagonal rule, no sum, no parity. If you’ve seen a sudoku that adds constraints (arrows, killer cages, thermometers), that’s a variant, and the variant rules are added on top of the one rule above.

A puzzle starts with some cells already filled in. These are called the givens (or clues). Your job is to fill in every other cell using only logic, in a way that satisfies the rule for every row, column, and box. A well-designed sudoku has exactly one solution, and you should never need to guess. If you find yourself guessing, the puzzle is either malformed or you’ve missed something.

What a beginner puzzle looks like

Difficulty in sudoku is not about how many cells are blank. It is about which logical techniques are required to solve it. A beginner-friendly puzzle is one solvable using only the simplest techniques, called singles. Roughly speaking, an easy puzzle gives you 35–45 starting clues; a harder puzzle gives you 22–28. But two puzzles with the same clue count can differ wildly in difficulty.

For your first puzzle, start with something explicitly labelled Easy. Don’t pick the “evil” difficulty out of ambition; you’ll bounce off the techniques and conclude that you’re bad at sudoku. You aren’t. You just haven’t learned them yet.

How to actually start

There are two beginner techniques, and together they will solve any easy puzzle. Master these and you can stop reading.

Technique 1: Hidden singles

A hidden single is a cell where, after looking at the row, column, and box, only one digit can possibly go. The phrase comes from the digit being “hidden” among other candidates until you scan carefully.

The simplest way to find them: pick a digit, say 5. Look at the board. Find every row, column, and box that already has a 5 in it. Now look for a 3×3 box that doesn’t have a 5. In that box, scan each empty cell and ask: is this cell in a row that already has a 5? Or a column that already has a 5? If so, rule it out. If only one cell in the box survives, that’s where the 5 goes.

This is sometimes called cross-hatching, because you’re mentally drawing lines through the rows and columns that already contain the digit, and seeing which cells in your target box aren’t crossed out. Most easy sudokus can be solved with cross-hatching alone.

Technique 2: Naked singles

A naked single is a cell where, after looking at every digit already in its row, column, and box, only one digit is left for that cell. You arrive at it from the cell’s perspective rather than the digit’s.

Pick an empty cell. Look at its row: which digits are present? Look at its column: which digits are present? Look at its box: which digits are present? Combine all three lists. Whatever is missing is the answer for that cell, provided exactly one digit is missing. Naked singles tend to fall into your lap late in a puzzle, after enough other cells are solved that you suddenly find one with only a single survivor.

Pencil marks: when and how

Once a puzzle gets even slightly harder than “easy,” you’ll need to keep notes. The standard tool is the pencil mark: small candidate digits written in the corner of a cell, listing every digit that could still go there.

On paper, write tiny digits in the corner of each empty cell. In an app, this is usually a notes mode, often a long-press or a separate button. As you place digits, you’ll erase the impossibilities from neighbouring cells’ pencil marks. When a cell’s pencil marks shrink to a single digit, that’s your naked single, ready to place.

A common beginner mistake is to fill in pencil marks for every cell on the board before placing a single answer. This is exhausting and usually unnecessary. Solve the obvious cross-hatched cells first. Bring in pencil marks when the obvious moves run out. In our beginner tips we cover the right cadence in more detail.

A guided first puzzle, in plain language

You don’t need a printed puzzle in front of you for this part; the sequence is what matters. Here is the workflow that experienced solvers run on every easy puzzle:

1. Take stock. Look at the board for ten seconds. Where are the densely filled rows, columns, and boxes? Those are your starting points. They have the most constraints already in place, so they will yield the easiest deductions.
2. Hunt by digit. Pick the digit that appears most often in the givens. Cross-hatch every box that doesn’t yet contain it. Place every hidden single you find. Move to the next most common digit. Repeat for all nine digits.
3. Cycle. Each placement creates new constraints. When you finish a digit-by-digit sweep, start over from the top. Some hidden singles only appear after you’ve placed earlier ones.
4. Switch perspective. When the digit-by-digit sweep stops yielding placements, switch to scanning empty cells for naked singles. Often three or four are sitting there waiting.
5. Add pencil marks selectively. If you’re stuck, add pencil marks, but only to the most constrained row, column, or box (the one with the fewest empty cells). Often that alone reveals the next step.

Most easy puzzles complete in under fifteen minutes once you have the rhythm. A common moment in beginner sudoku is realising, roughly halfway through, that the rest of the puzzle “falls out” almost on its own. That’s the constraint cascade doing its work.

What to do when you’re stuck

Three things almost always solve a beginner’s stuck puzzle:

1. Re-scan the most-placed digit. If you’ve placed seven of the nine 5s, the remaining two are usually forced but easy to miss.
2. Pencil-mark a single box. Pick the box closest to full. Write candidates only inside that box. Often a digit appears as a candidate in only one cell, and that is a hidden single you missed by eye.
3. Walk away for five minutes. This sounds glib but isn’t. Visual fatigue is real, and a fresh look usually surfaces the move you missed. If it doesn’t, you may have made an earlier mistake; restart the cell that feels uncertain rather than throwing the whole puzzle out.

What you should not do

• Don’t guess. A correctly designed sudoku can always be solved by logic. Guessing teaches you nothing and tends to corrupt the rest of the puzzle when the guess is wrong.
• Don’t add up rows. The digits sum to 45 in every row, column, and box, and that fact is almost never useful. Skip the arithmetic.
• Don’t fix mistakes by erasing the latest digit. If you’ve hit a contradiction, the wrong digit was probably placed several moves ago. The honest fix is to undo back to a point you are sure about, or restart.

Where to go from here

Once easy puzzles feel routine, your next jump is medium and hard difficulty, where you’ll need techniques beyond singles. The most useful next ones are naked pairs, locked candidates, and eventually X-Wings. We have a full illustrated guide in Sudoku Solving Techniques.

If you’d like to know what you’re actually getting from a daily puzzle, cognitively, neurologically, and emotionally, we cover the research in The Benefits of Sudoku. And if you’re curious about where this addictive little grid came from, the surprisingly winding history of sudoku is worth a read.