How to solve Sudoku: a beginner's guide

A step-by-step beginner's guide to solving Sudoku — what the rules really mean, the two techniques you need first, and why most blanks have only one possible answer.

Sudoku looks more intimidating than it is. The whole puzzle rests on a single, easy-to-state rule: every row, every column, and every 3×3 box must contain the digits 1 through 9 exactly once. That's it. Once you internalise the rule, every blank in a Sudoku has a finite (often very small) set of legal candidates, and most of the puzzle is just finding the cell where there's only one.

Read the grid before you write

Beginners reach for the pencil too early. Spend the first thirty seconds scanning instead. Notice which digits already appear most often — there are usually one or two that are nearly complete. Solving those digits first cascades into more constraints elsewhere, which collapses the puzzle faster than starting at the top-left and pushing right.

Technique 1: Scanning

Pick a digit that already appears at least three times. For each 3×3 box that doesn't yet contain it, ask: which cells in this box could legally hold this digit, given the rows and columns it already appears in? Often the answer is a single cell — write it in.

Repeat for every digit. A clean scan usually fills four to six cells on an “Easy” puzzle, and changes the board enough that you can scan again and find more.

Technique 2: Naked singles

Look at any blank cell. Cross off every digit that already appears in its row, column, or box. If exactly one digit survives, write it in. Naked singles are the bread and butter of Sudoku — every “Easy” puzzle is solvable by alternating scanning and naked-single hunts until the grid is full.

When the easy moves run out

On Medium and harder puzzles, scanning eventually stops finding moves. That's when you reach for the named strategies — naked pairs, hidden singles, pointing pairs. They have intimidating names but the underlying logic is the same: each one rules out candidates by spotting a constraint humans miss on the first pass. We covered them in our Sudoku strategies post.

The most useful habit

Mark candidates lightly when you're stuck. A pencil-mark of “this cell could be 3 or 7” lets you see, at a glance, when a 3 elsewhere in the row eliminates one option and gives you a naked single. Most Sudoku apps (including the one on the puzzle page) handle the candidate marks for you.

That's really it. Three rules, two techniques, one habit. The difficulty rating on a Sudoku is mostly about how many naked singles you have to find before the harder strategies become necessary. On an “Easy” puzzle you may never need them.