How to Solve Sudoku — Complete Beginner's Guide (2026)

The rules of Sudoku (in one paragraph)

A Sudoku board is a 9x9 grid divided into nine 3x3 boxes. The rules are simple: fill every empty cell with a digit from 1 to 9 so that every row contains all nine digits exactly once, every column contains all nine digits exactly once, and every 3x3 box contains all nine digits exactly once. That is the whole game. The puzzle you are given starts with some cells filled in as "clues" — a well-designed Sudoku has exactly one solution, which you can find with logic and no guessing. Try a beginner board on Sudoku Classic if you want to work through the techniques below with a real puzzle in front of you.

Nothing about Sudoku is mathematical in the arithmetic sense. The digits 1 through 9 are just nine distinct symbols; you could play the same game with the letters A through I and it would be identical. Sudoku is pure combinatorial logic, which is why it feels so satisfying — every step you take is provable, and every completed board is a small proof you built yourself.

Technique 1: Scanning (find the easy ones first)

Every Sudoku solve starts with scanning. Pick a digit, say 1, and look at each row, column, and box to find where 1 must go. If a box already contains a 1 in one cell, and the other cells in that box either share a row or column with another 1 elsewhere on the board, you can often narrow the location of a missing 1 down to exactly one cell. Do this for every digit, one at a time, and you will typically place 15 to 25 clues on an easy puzzle in the first pass.

The classic beginner mistake is to jump around trying to fill any cell that "looks obvious" rather than systematically scanning one digit at a time. The systematic scan is faster because it uses the same working memory (where does 1 go?) across many cells before moving to a new digit. When you have scanned every digit and cannot place anything new, you are ready for the next technique.

Technique 2: Naked singles (the workhorse move)

A "naked single" is a cell where only one digit can legally go. To find them, look at an empty cell, check every digit already present in its row, column, and 3x3 box, and mark down the digits that are not yet used. If that list contains exactly one digit, you have found a naked single — that cell must be that digit. This is the single most productive technique in beginner Sudoku, and on easy boards it will finish the puzzle for you.

The efficient way to spot naked singles is to focus on rows, columns, or boxes that already have many clues. A row with seven filled cells has only two empty cells, and the missing two digits are strongly constrained. You will often find that one of those two empty cells has only one legal option because of pressure from its column or box. Naked singles compound: every one you place changes the constraints on adjacent cells, and you will often chain three or four together in a row.

Technique 3: Hidden singles (harder to see)

A "hidden single" is a digit that can only legally go in one cell within a given row, column, or 3x3 box — even if that cell has multiple candidates on the surface. Example: suppose the digit 7 has candidates in three cells of a row on your pencil-marks, but two of those cells are in the same column as another 7 already placed elsewhere. That leaves only one cell in the row where 7 can legally go — so 7 must be there, even though that cell might have candidates for 3, 5, and 7 in isolation.

Hidden singles are what separate players who solve easy boards from those who solve medium ones. The trick to finding them is to focus on a single digit at a time and ask "where can this digit go in this row?" rather than "what can go in this cell?" Alternate between the naked-single view (cell-first) and the hidden-single view (digit-first) as you scan the board. A puzzle that looks stuck to a naked-singles-only player often opens up immediately when you switch modes.

Technique 4: Naked pairs and hidden pairs

A "naked pair" is when two cells in the same row, column, or box have exactly the same two candidates — say both cells have "{3, 8}" as their only options. You do not know which is 3 and which is 8, but you know for certain that 3 and 8 occupy those two cells. That means you can remove 3 and 8 as candidates from every other cell in the same row/column/box. This does not directly place a digit, but it often unlocks a naked or hidden single elsewhere.

A "hidden pair" is the digit-first version: if two digits, say 4 and 9, can only appear in the same two cells within a row/column/box, then those two cells must contain 4 and 9 in some order — and you can eliminate every other candidate from those cells. Both techniques are essential for medium and hard puzzles. Practice them by keeping careful pencil marks (candidate lists) in every empty cell. On a browser Sudoku like Sudoku Classic, the interface usually offers a notes mode that does this bookkeeping for you.

Technique 5: Box-line reduction (pointing pairs)

Box-line reduction, also called "pointing pairs" or "pointing triples", is the last beginner-friendly technique. It works like this: if all candidates for a particular digit within a 3x3 box are confined to a single row or column, then that digit must be somewhere on that row/column within that box — and can be removed as a candidate from that row/column outside the box. Example: if 5 in the top-left box can only go in cells of the top row, then 5 cannot appear anywhere else in the top row across the puzzle.

Box-line reduction sounds abstract but it triggers surprisingly often, especially in the middle of a hard puzzle where every other technique has stalled. It is the bridge from beginner to intermediate Sudoku. Once you have naked singles, hidden singles, naked pairs, hidden pairs, and box-line reduction in your toolkit, you can solve 95% of newspaper Sudokus without ever guessing.

A practical solving order (do this every time)

Follow this order and you will solve puzzles faster with fewer mistakes. Start with a full scan for each digit 1 through 9, placing every obvious hidden single you find. Then fill in candidate pencil marks for every remaining empty cell — this is the setup for every advanced technique. Next, sweep for naked singles across the whole board. Then sweep for hidden singles by digit. Then look for naked and hidden pairs. Finally, look for box-line reductions. Loop through this order until the board is complete.

The most common beginner mistake is jumping ahead — trying to find naked pairs before you have exhausted all naked singles, for example. The techniques stack: harder techniques become easier when the easier techniques have removed enough candidates first. Discipline matters more than cleverness in Sudoku. See our guide to how to get higher 2048 scores for a similarly structured strategy walkthrough in a different puzzle.

• Full digit scan (1 through 9)
• Place obvious hidden singles
• Fill pencil-mark candidates in every empty cell
• Sweep for naked singles
• Sweep for hidden singles
• Look for naked and hidden pairs
• Look for box-line reductions
• Loop until complete

How long should each difficulty take?

As a rough benchmark once you have the techniques above: an easy Sudoku should take about seven minutes, a medium about fifteen, a hard about twenty-five, and an expert forty or more. If an easy puzzle is taking you thirty minutes, you are not yet fluent with hidden singles — practice with three easy boards a day for a week and the time will drop. If a hard puzzle is taking you two hours, you probably need to learn one intermediate technique beyond this guide (X-Wing is the traditional next step). Do not use guess-and-check. A well-designed Sudoku never requires guessing, and the habit of guessing prevents you from developing the pattern recognition that makes hard puzzles feel easy.