How to play Sudoku—from your first square to your first solve.
Sudoku is a logic puzzle, not a maths test. Your job is to fill every empty cell so each row, column, and 3×3 box contains the digits 1 through 9 exactly once. This guide teaches the rules first, then lets you practise every idea on a real grid.
No guessing. No arithmetic. Just a clear sequence of certain moves.
Reviewed and rebuilt July 22, 2026
One square. One certain answer.
The highlighted row already has 1, 2, 4, 5, 6, 7, 8, and 9. Which digit is missing?
Look only at the highlighted row. You do not need to inspect the rest of the puzzle yet.
Sudoku rules: the complete beginner version
A standard Sudoku has 81 cells arranged in nine rows, nine columns, and nine 3×3 boxes. Some cells start with numbers; these are givens and never change. You fill the remaining cells.
The goal is not to make rows add up to a total. The digits behave like nine different symbols. Only their placement matters.
The three rules every move must obey
Each rule applies at the same time. A candidate is legal only when it creates no repeat in its row, column, or box.
Every row contains 1–9
Read horizontally. Each digit appears exactly once, so a row can never contain two 5s, two 8s, or any other duplicate.
Every column contains 1–9
Read vertically. Columns follow the identical no-repeat rule, from the top cell to the bottom cell.
Every 3×3 box contains 1–9
The nine bold-outlined boxes also need all nine digits once. A move must fit its box as well as its row and column.
See which cells affect each other
Choose a view, then select any cell. The highlight shows the unit or peers you need to inspect before making a move.
A row runs left to right. The selected cell shares this row with eight other cells.
Spot the duplicate
Each tiny position shows one given 5 and one proposed move outlined in red. Name the rule the move would break.
Question 1/3: Which rule does the outlined 5 break?
Know the board
- Cell
- One square in the grid. R4C7 means row 4, column 7.
- Unit
- Any complete row, column, or 3×3 box.
- Given
- A number supplied by the puzzle. It cannot be moved or changed.
- Peer
- A cell in the same row, column, or box as another cell.
- Candidate
- A digit that could legally fit in an empty cell.
- Placement
- A digit proved to belong in a cell—not a guess.
How do you actually solve a Sudoku?
You solve by elimination. Every given blocks that digit from its peers. The remaining legal digits are candidates. When only one placement survives, the move is certain.
Scan a unit
Pick a row, column, or box and compare what is present with the digits 1 through 9.
Rule out impossibilities
A digit cannot go in a cell if it already appears in that cell’s row, column, or box.
Place only what is proved
A move is ready when one digit has one legal cell, or one cell has one legal digit.
Update the board
Each placement changes its peers. Remove stale candidates and scan again; the puzzle gets easier as it fills.
Two beginner questions that sound similar
What digit is missing from this unit?
Last digit / full houseEight cells are filled, so the ninth digit is whatever 1–9 value is absent.
Where can this digit go in this unit?
Last position / hidden singleSeveral cells may be empty, but crossing rows, columns, or boxes leave the chosen digit one possible home.
What can go in this cell?
Naked singleCheck the cell against all three units. If eight digits are blocked, its one remaining candidate is the answer.
Your first six Sudoku lessons
The lesson gives you less help as you progress: first a nearly complete row, then a hidden placement, candidate notes, a naked single, three guided moves, and a final check. Your progress is kept on this device.
Beginner course progress
Lesson 1/6: Last digit
Complete a nearly finished row
The easiest move in Sudoku is sometimes called a full house: eight cells in a unit are filled, so exactly one digit is missing. Compare the row with 1 through 9.
Which digit belongs in the highlighted cell?
When—and how—to use pencil marks
You do not need notes for a nearly complete unit. Add them when easy scanning stops and several cells have multiple possibilities. Good notes reduce mental load; stale or excessive notes create noise.
- 01
Choose one empty cell
Inspect its row, column, and box. Start with all digits 1–9 as possibilities.
- 02
Remove visible digits
Cross out any digit already present in one of those three units.
- 03
Write the survivors small
The remaining digits are candidates, not guesses or promises.
- 04
Update after every placement
When a digit is placed, remove it from notes in all peer cells immediately.
Useful notes
- Contain only legal candidates
- Are updated after every placement
- Make singles and pairs easier to see
Misleading notes
- Include digits already present in a peer
- Stay unchanged after the board changes
- Are treated as possible answers without proof
The Sudoku solve loop: scan, prove, place, repeat
Use the same loop after every move. It prevents random wandering and tells you when you are genuinely ready for a new strategy.
- 1
Scan the busiest units
Rows, columns, and boxes with many givens have fewer missing digits and are usually easiest to finish.
- 2
Look for last digits and last positions
Ask both questions: what digit is missing here, and where can this chosen digit still go?
- 3
Check cells for naked singles
Combine row, column, and box restrictions. Place any cell with one legal candidate.
- 4
Update candidates immediately
A new digit eliminates itself from every peer. Clean notes before searching for another pattern.
- 5
Start the scan again
A placement that looks small can unlock several units. Re-run the easy checks before escalating.
- 6
Use one new technique at a time
If no singles remain, move to pairs or box-line interactions—then return to the basic loop after every elimination.
Diagnose the board before learning a harder trick
Stuck is a symptom, not a strategy level. Identify what is stopping you and use the smallest useful intervention.
I have not used notes yet
Add candidates to the emptiest-looking cells or one full unit.
The next single may be invisible because you are holding too many possibilities in your head.
My notes are everywhere
Re-check and remove candidates invalidated by recent placements.
Stale notes can hide a naked single or make a valid pattern look impossible.
I keep scanning the same area
Switch from cells to digits: choose one digit and trace its possible positions through every box.
Changing the question often reveals a hidden single.
Nothing has one candidate
Check for a pair or a box-line interaction, then return to singles.
A small elimination is often enough to restart the beginner loop.
The board contradicts itself
Undo to the last certain move and inspect the first guess or stale note.
A valid puzzle does not need a contradiction to make progress.
Five beginner mistakes—and the better habit
Guessing when a scan feels slow
Use candidates and prove one elimination at a time.
Checking only the row
A digit must fit the row, column, and box simultaneously.
Adding every note immediately
Start with obvious scans; add notes when they reduce real mental load.
Leaving notes stale
Treat note cleanup as part of every placement.
Chasing advanced patterns too early
Re-scan for singles after every elimination or placement.
A strategy path that grows with you
Do not memorise every named pattern at once. Learn the smallest technique that solves the puzzles you are playing, and keep returning to the basic loop.
- Naked singlesStart hereA cell has one remaining candidate after all peer restrictions are applied.Open guide
- Hidden singlesStart hereA digit has one possible home inside a row, column, or box.Open guide
- Pencil marksFoundationBuild and maintain candidate lists that reveal the next deduction.Open guide
- Cross-hatchingBeginnerUse crossing rows and columns to narrow a digit’s position inside a box.Open guide
- Naked pairsNext stepTwo cells reserve the same two digits, eliminating them from other cells in the unit.Open guide
- Pointing pairsNext stepCandidates locked to one line inside a box eliminate that digit farther along the line.Open guide
Sudoku beginner questions
Clear answers to the questions that usually appear during a first solve.
Is Sudoku a maths game?
No. Sudoku uses digits as nine distinct symbols. You never need to add, subtract, multiply, or calculate a total; only the no-repeat placement rules matter.
Can a Sudoku have more than one solution?
A properly constructed standard Sudoku should have one unique solution. If a puzzle has no solution or several solutions, it is not a valid standard puzzle.
Should beginners ever guess?
You do not need to guess in a well-formed puzzle designed for logical solving. If you feel forced to guess, first check for a missed single, stale note, or a technique appropriate to the difficulty.
When should I start using pencil marks?
Use notes when simple visual scans stop producing placements and you can no longer track legal candidates comfortably. You can solve very easy openings without filling every empty cell with notes.
What is the easiest Sudoku technique?
Start with a last digit in a nearly complete unit. Next learn last positions, naked singles, and hidden singles. These techniques solve a large share of beginner puzzles.
Why can’t a digit repeat in a different 3×3 box?
Repeats are checked per unit. A digit may appear many times across the whole grid, but never twice in the same row, column, or 3×3 box.
What makes one Sudoku harder than another?
Difficulty depends on the deductions required, not simply the number of givens. A sparse puzzle can be easy, while a fuller puzzle may require advanced candidate patterns.
How do I get faster at Sudoku?
Build accuracy first. Scan units in a repeatable order, update notes immediately, and recognise singles without re-proving them several times. Speed follows pattern recognition.
Solve an easy Sudoku while the loop is fresh
Start with rows, columns, and boxes that are nearly complete. Place only certain moves, update the board, and return to the loop whenever you pause.