To play Sudoku, fill the empty cells with digits 1–9 while keeping every row, column, and 3×3 box free of repeats.
The easiest way to begin is not to stare at all 81 cells. Find one area with very little left to solve, make a placement only when the grid forces it, then use that new digit to unlock the next move.
For a first puzzle, think in a simple loop:
look → rule out → place → re-scan.
Step 1: Understand the grid
A classic Sudoku has:
- 9 rows
- 9 columns
- 9 boxes, each measuring 3×3 cells
- 81 cells in total
Every empty cell belongs to one row, one column, and one box at the same time.
Step 2: Look for nearly complete areas
When you are new to Sudoku, a good first move is to scan areas that already contain many digits.
Suppose a row contains:
1 2 3 4 5 6 7 _ 9
The only missing digit is 8, so the empty cell must contain 8.
This is the simplest form of Sudoku deduction: identify what is missing and check that the position is consistent with the row, column, and box.
Step 3: Scan rows, columns, and boxes together
Most moves are not as obvious as an eight-filled row.
Choose a digit — for example 5 — and look at where 5 already appears. Existing 5s block other cells in their rows, columns, and boxes.
Inside a box, those restrictions may leave only one place where another 5 can go.
This general process is called scanning. A common beginner form of it is crosshatching, where row and column restrictions help you find the only position for a digit inside a box.
Step 4: Use elimination
For any unsolved cell, consider the digits 1–9.
Remove every digit that already appears in the cell's row, column, or box. Whatever remains is still possible.
If only one candidate remains, you have found a Naked Single and can place it.
If a digit can go in only one cell within a row, column, or box — even if that cell has other candidates written in it — you have found a Hidden Single.
You do not need to memorize those names before playing, but the concepts become useful very quickly.
Step 5: Add candidates when you need them
On easy puzzles, scanning may reveal enough moves without writing anything inside empty cells.
When the puzzle becomes less obvious, you can use pencil marks or notes to record candidates.
For example:
{2, 7}
inside a cell means that, based on the current grid, 2 and 7 are the remaining possibilities you are tracking for that cell.
Candidates do not mean you should choose one at random. They are information you can use in later deductions.
Step 6: Re-scan after every useful move
Sudoku is iterative.
A placement that solves one cell can:
- complete a row
- remove a candidate from several peers
- reveal a Hidden Single in a box
- create a pair or another pattern elsewhere
After placing a digit, look again at the affected row, column, and box before moving to a completely different part of the grid.
A simple beginner solving loop
Use this loop whenever you are unsure what to do next:
- Scan for a row, column, or box with one missing digit.
- Scan individual digits across boxes.
- Look for cells with only one candidate.
- Look for digits that have only one possible position in a unit.
- Update candidates if you use notes.
- Repeat from the top.
As your skill improves, intermediate and advanced techniques extend this loop rather than replacing it.
What should you do if you get stuck?
First, do not assume you need to guess.
Re-check:
- units with many solved cells
- boxes where a digit has only two or three possible positions
- candidate lists that changed after your last placement
- Naked Singles and Hidden Singles you may have missed
If no basic move remains, the puzzle may require an intermediate technique such as Locked Candidates or a subset like a Naked Pair.
Common beginner mistakes
Ignoring the box
A digit can be absent from the row and column but still be blocked by the 3×3 box.
Treating a possible digit as a solved digit
If a cell can contain 2 or 7, neither one is proven simply because both are legal.
Forgetting to update notes
Old candidates can make later patterns look valid when they are not. If a placed digit removes a candidate from its peers, the notes need to reflect that.
Looking at only one part of the grid for too long
A Sudoku is interconnected. When one area stops producing progress, another area may contain an easier move that unlocks it later.
FAQ
Where should I start a Sudoku?
Start with rows, columns, or boxes that already contain many digits, then scan for digits with very limited positions.
Should I fill in all candidates immediately?
Not necessarily. Many players begin with scanning and add candidates when the puzzle stops producing obvious placements.
What is the easiest Sudoku technique?
Finding the last missing digit in a unit and identifying Naked Singles or Hidden Singles are among the most accessible logical moves for beginners.
What if I make a mistake?
In a digital game you can usually undo the move. More importantly, try to identify which rule or assumption failed so the correction teaches you something.
What to learn next
Continue with How to Solve Sudoku for a more systematic solving process. Then learn Scanning, Sudoku Candidates, Naked Singles, and Hidden Singles.