Sudoku may look intimidating with its 81 empty cells, but every puzzle — even the hardest ones — is built on a foundation of simple beginner strategies. Master these seven techniques and you will be able to solve any Easy puzzle and most Medium puzzles with confidence. No guessing, no math, just pure logic.
If you have not learned the basic rules yet, start with our How to Play Sudoku guide first. Already comfortable with the rules? Read on.
Strategy 1: Last Free Cell
The last free cell is the simplest Sudoku strategy and the perfect starting point for beginners.
How it works: When eight of the nine cells in a row, column, or 3x3 box are already filled, the ninth cell must contain the one missing digit. You do not need to consider candidates or do any elimination — just determine which number from 1 to 9 is missing.
When to use it: Look for rows, columns, or boxes that are nearly complete. Puzzles with many givens (starting numbers) will have plenty of last-free-cell opportunities right from the start.
Example: If a row contains 1, 2, 3, 4, 5, 7, 8, 9 and one empty cell, that cell must be 6.
This technique cascades beautifully: filling one last free cell often creates another last free cell in a crossing row, column, or box.
Strategy 2: Naked Single
The naked single (also called an “obvious single” or “sole candidate”) is the most fundamental solving technique in Sudoku.
How it works: Fill in pencil marks (candidate numbers) for an empty cell by checking which digits already appear in its row, column, and box. If only one candidate remains, that digit must go in that cell.
When to use it: After filling in last free cells, scan for cells with only one possible value. On Easy puzzles, naked singles alone can often solve most of the grid.
Step-by-step:
- Pick an empty cell.
- Check its row — which digits are already placed?
- Check its column — which digits are already placed?
- Check its 3x3 box — which digits are already placed?
- Combine all placed digits. If only one is missing from 1–9, that is your answer.
Tip: Start with cells at the intersection of rows, columns, and boxes that are already heavily filled. These are most likely to yield naked singles.
Strategy 3: Hidden Single
The hidden single is your second essential technique. It is sometimes harder to spot than a naked single because the target cell may have multiple candidates.
How it works: Within a row, column, or box, look for a digit that can only go in one cell. Even if that cell has several candidates, the digit must go there because no other cell in that unit can hold it.
When to use it: After naked singles stop producing placements, switch to scanning units (rows, columns, boxes) for digits that have only one legal position.
Step-by-step:
- Pick a row, column, or box.
- For each digit 1–9 that is not yet placed in that unit, check which empty cells could hold it.
- If a digit has only one possible cell, place it there.
The difference from naked singles: A naked single looks at one cell and asks “what can go here?” A hidden single looks at one unit and asks “where can this digit go?” Both approaches find placements, but hidden singles often uncover moves that naked singles miss.
Strategy 4: Pencil Marks (Candidate Notation)
Pencil marks are not a solving technique by themselves, but they are the foundation every other strategy builds on. Learn them early and you will progress much faster.
How it works: In each empty cell, write small numbers representing every digit that could still go there based on current constraints. As you solve cells, update the pencil marks by removing digits that are no longer possible.
Why they matter:
- They make patterns visible that are impossible to spot mentally.
- They enable pair and triple techniques.
- They prevent the errors that come from trying to hold too much in your head.
Tip: On Easy puzzles, you can often get by without pencil marks. Start using them on Medium puzzles — that is where they become essential. For a complete guide, see Pencil Marks Explained.
Strategy 5: Naked Pair
The naked pair is your gateway to intermediate solving and the first technique that uses pencil marks for elimination.
How it works: If two cells in the same row, column, or box contain exactly the same two candidates and nothing else, those two digits are “claimed” by those two cells. You can eliminate those two digits from all other cells in that unit.
Example: If two cells in a box both contain only {3, 7}, then 3 and 7 must go in those two cells (in some order). Remove 3 and 7 from the pencil marks of all other cells in that box.
Why it is powerful: The elimination often reveals naked singles or hidden singles in the remaining cells, creating a cascade of placements.
Related techniques: Naked triples and naked quads extend the same logic to three or four cells.
Strategy 6: Hidden Pair
The hidden pair works like the reverse of a naked pair. It is slightly harder to spot but equally powerful.
How it works: If two digits appear as candidates in only two cells within a row, column, or box, those two digits must go in those two cells. You can remove all other candidates from those two cells.
Example: In a box, suppose digit 4 appears in only cells A and B, and digit 8 also appears in only cells A and B. Even if those cells have other candidates like {2, 4, 7, 8}, you know 4 and 8 must occupy cells A and B. Remove 2 and 7 from those cells, leaving {4, 8} in each.
Tip: Hidden pairs are often obscured by extra candidates. Scan systematically — for each pair of digits in a unit, check how many cells contain them.
Strategy 7: Hidden Triple
The hidden triple extends the hidden pair logic to three digits and three cells. It is the most advanced beginner technique.
How it works: If three digits appear as candidates in only three cells within a unit, those three digits are locked to those cells. Remove all other candidates from those three cells.
This technique is challenging because the three digits do not all need to appear in every cell. Two of the three cells might contain all three digits while the third cell contains only two of them. The key is that those three digits appear nowhere else in the unit.
Putting It All Together: A Solving Workflow
Here is the recommended order for applying these strategies:
| Step | Strategy | What to Look For |
|---|---|---|
| 1 | Last Free Cell | Rows, columns, or boxes with 8 of 9 filled |
| 2 | Naked Single | Cells with only one candidate |
| 3 | Hidden Single | Digits with only one possible cell in a unit |
| 4 | Naked Pair | Two cells in a unit sharing the same two candidates |
| 5 | Hidden Pair | Two digits confined to the same two cells in a unit |
| 6 | Hidden Triple | Three digits confined to three cells in a unit |
| 7 | Repeat | Go back to Step 1 after every elimination |
After each placement or elimination, always re-scan for naked singles and hidden singles. Eliminations from pairs and triples frequently create new singles.
Common Beginner Mistakes
- Forgetting to check all three units. Always check the row, column, AND box before placing a digit. Checking only two can lead to errors.
- Not updating pencil marks. When you place a digit, immediately remove it from the pencil marks of all cells in the same row, column, and box.
- Guessing. If you cannot find a logical placement, you have missed something. Go back and re-scan rather than guessing.
- Starting with empty areas. Focus on rows, columns, and boxes with the most filled cells — they have the fewest candidates and yield placements fastest.
- Trying to solve the whole grid at once. Work one unit at a time. Patience and systematic scanning always win.
What Comes Next?
Once you are comfortable with these seven strategies, you are ready to move beyond Easy puzzles. Here is your progression path:
- Medium puzzles — Require pointing pairs and box-line reduction
- Hard puzzles — Introduce X-Wing and Swordfish
- Expert puzzles — Add XY-Wing and coloring
- Evil puzzles — Demand chains and unique rectangles
For a complete map of what to learn and when, see our Sudoku Technique Progression guide or start the structured Learning Path.
Frequently Asked Questions
What is the easiest Sudoku strategy for beginners?
The easiest strategy is the last free cell — when a row, column, or box has eight digits filled, the ninth cell must contain the missing digit. After that, naked singles are the most straightforward technique: find a cell where only one digit is possible.
What are pencil marks and should beginners use them?
Pencil marks are small candidate numbers written in a cell to track which digits could go there. On Easy puzzles you can often skip them, but they become essential on Medium and above. Learning to use them early builds good solving habits. See our pencil marks guide for a full walkthrough.
How do I know which strategy to use?
Start simple and escalate. First scan for last free cells and naked singles. Then look for hidden singles. If you are still stuck, check for naked pairs and hidden pairs. Only move to more advanced techniques when simpler ones stop working. Our solving checklist provides a systematic approach.
What is the difference between a naked single and a hidden single?
A naked single is a cell with only one candidate left. A hidden single is a digit that can only go in one cell within a row, column, or box — even though that cell may have multiple candidates. Both place a digit, but hidden singles require looking at the whole unit rather than just one cell.