Sudoku Tips for Beginners: 7 Techniques to Solve Every Puzzle
Sudoku looks intimidating at first — a grid full of empty cells and just a handful of numbers to go on. But the rules are simpler than they appear, and every single Sudoku puzzle has exactly one correct solution reachable through pure logic. No guessing required. These seven techniques will take you from complete beginner to confident solver.
The Three Rules of Sudoku
Before techniques, the rules. A standard 9×9 Sudoku grid is divided into nine 3×3 boxes. Your goal is to fill every empty cell with a number from 1 to 9, following three constraints:
- Every row must contain the numbers 1–9 with no repeats.
- Every column must contain the numbers 1–9 with no repeats.
- Every 3×3 box must contain the numbers 1–9 with no repeats.
That is the entirety of Sudoku's rules. Everything else — all the strategy and technique — is about using these three constraints cleverly to deduce where each number must go.
Technique 1: Scanning (Your Most-Used Tool)
Scanning means looking across rows, columns, and boxes to find cells where only one number can possibly go. Start your every puzzle with a scanning pass before using any other technique.
For each number 1–9, look at where it already appears on the board. Each existing placement eliminates that number from its entire row, column, and box. When a cell's row, column, and box account for eight of the nine numbers, the ninth number is the cell's answer — no calculation required.
Beginners are often surprised how many cells can be solved by scanning alone on easy and medium Sudoku puzzles. Develop the habit of scanning every number from 1 to 9 at the start of each session.
Technique 2: Cross-Hatching
Cross-hatching focuses on placing a specific number within a box by elimination. Choose a number — say, 7. Look at the three rows that pass through the box you are targeting. If 7 already appears in two of those rows (anywhere in those rows), then 7 can only go in the one remaining row within your target box. If that row has only one empty cell in the box, you have found your placement.
Work through each number from 1 to 9 for each box. Cross-hatching is particularly powerful in the early game when large sections of the board are empty, because each existing number gives you a constraint to exploit.
Technique 3: Single Candidates
A single candidate is a cell where only one number is possible when you consider all three constraints simultaneously — its row, its column, and its box. This technique requires pencil marks: small candidate numbers written in the corner of each empty cell listing every number that could go there.
To find single candidates, go through each empty cell and list which numbers 1–9 are not already in its row, column, or box. If only one number remains, you have a definite placement. PuzzlyNest's Sudoku Classic includes a built-in pencil mark mode — tap the pencil icon before entering a number to toggle candidate notation.
Technique 4: Naked Pairs
A naked pair occurs when two cells in the same row, column, or box each contain exactly the same two candidates — and no others. When this happens, those two numbers are “spoken for” by those two cells. Neither number can appear anywhere else in that row, column, or box, allowing you to remove them from all other cells' candidate lists.
Example: if cell A and cell B in the same row both show only {4, 7} as candidates, you know 4 and 7 will fill those two cells (in some order). Every other cell in that row can have 4 and 7 removed from its candidates, which often reveals new single candidates elsewhere.
Naked pairs are the gateway to intermediate Sudoku. Once you can spot them reliably, medium-difficulty puzzles become significantly more tractable.
Technique 5: Hidden Singles
A hidden single is when a particular number can only go in one cell within a row, column, or box — even though that cell has multiple candidates listed. The number is “hidden” among other candidates but is actually forced.
To find hidden singles, work number by number rather than cell by cell. For each number 1–9, look at each row, column, and box and ask: in how many cells could this number go? If the answer is one, place it immediately. Hidden singles are extremely common in medium and hard puzzles and are often the key that unlocks an otherwise stuck board.
Technique 6: Pointing Pairs
Within a 3×3 box, if a number's candidates are all confined to a single row or column inside that box, then that number cannot appear elsewhere in that row or column outside the box. You can eliminate it from all other cells in the row or column beyond the box.
This technique is subtler than the previous ones but very powerful in hard puzzles. If candidates for the number 3 in a box all sit in the top row of that box, then 3 cannot appear in the rest of that row — even in cells belonging to other boxes. Use this to prune candidate lists significantly.
Technique 7: Box/Line Reduction
The reverse of pointing pairs: if a number's candidates within a row or column are all confined to a single box, then that number cannot appear elsewhere in that box. You can eliminate it from all other cells in the box that are not on that row or column.
Box/line reduction is a fundamental “intermediate” technique and the last one you need before tackling hard puzzles confidently. Combined with the six techniques above, it handles the vast majority of cells in standard Sudoku puzzles up to hard difficulty.
Putting It All Together: A Solving Order
When you sit down with a new Sudoku puzzle, follow this order:
- Scan each number 1–9 across all rows, columns, and boxes for immediate placements.
- Cross-hatch each box for numbers that are restricted to one row or column.
- Fill in pencil marks for all remaining empty cells.
- Find single candidates — cells with only one pencil mark.
- Look for hidden singles, naked pairs, pointing pairs, and box/line reduction to prune candidates further.
- Repeat from step 4 — each new placement creates new constraints and often reveals more singles.
The key insight is that every technique feeds the others. A naked pair eliminates candidates, which creates new single candidates, which trigger new cross-hatching opportunities. The board opens up progressively as you apply each technique in sequence.
Start with Sudoku Mini (a 6×6 grid) to practise scanning and single candidates before moving to the full 9×9 Sudoku Classic. Both are completely free to play on PuzzlyNest.
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