The Naked Single is the simplest and most fundamental technique in Sudoku solving. It's the first technique every solver learns, and despite its simplicity, it remains essential throughout your Sudoku journey. In this interactive guide, you'll master this technique with visual demonstrations!
💡 Key Concept
A Naked Single occurs when a cell has only one possible candidate remaining. After eliminating all impossible digits (those already in the same row, column, and box), if only one number can fit — that's your Naked Single!
🔍 What is a Naked Single?
The logic behind a Naked Single is beautifully simple:
- Look at an empty cell
- Check its row — which numbers are already used?
- Check its column — which numbers are already used?
- Check its 3×3 box — which numbers are already used?
- Eliminate all used numbers from 1-9
- If only ONE number remains — you found a Naked Single!
The number "stands naked" in the cell because it's the only possibility — there's nowhere to hide!
📖 The Elimination Process
We systematically check the row, column, and box to eliminate impossible candidates. When only one candidate remains, we've found our Naked Single!
📝 The 4-Step Process
Follow this systematic approach to identify Naked Singles every time:
- Select an empty cell — Start with cells that have many filled neighbors
- List all possibilities — Begin with 1, 2, 3, 4, 5, 6, 7, 8, 9
- Eliminate used numbers:
- Cross out numbers in the same row
- Cross out numbers in the same column
- Cross out numbers in the same 3×3 box
- Count remaining candidates:
- Zero candidates → Error! There's a mistake somewhere
- Multiple candidates → Not a Naked Single (try another cell)
- Exactly one candidate → 🎉 Naked Single found!
📖 Visual Elimination
Candidates are shown as small numbers in empty cells. As we eliminate them, they get crossed out. The last remaining candidate is our answer!
⚖️ Naked Single vs Hidden Single
Understanding the difference between these two fundamental techniques is crucial:
| Aspect | Naked Single | Hidden Single |
|---|---|---|
| What you examine | A single cell's candidates | An entire row/column/box |
| The question | "What can go in this cell?" | "Where can this number go?" |
| Logic | Cell has only 1 candidate | Number has only 1 position |
| Visibility | Very obvious | Requires scanning |
| Difficulty | Easiest technique | Easy (with practice) |
🎯 Remember This
Naked Single: "This cell can ONLY be X" (cell-focused)
Hidden Single: "X can ONLY go in this cell" (number-focused)
📖 Expert Analysis
Each step demonstrates how eliminating candidates reveals the only possible number for a cell. This is pure logic — no guessing required!
💡 Pro Tips for Finding Naked Singles
🚀 Speed Up Your Solving
- Start with crowded areas: Cells surrounded by many filled cells are more likely to be Naked Singles
- Look at intersections: Where nearly-complete rows, columns, and boxes meet
- Use pencil marks: Write small candidates in cells to track possibilities
- After each placement: Check neighboring cells — new Naked Singles often appear
- Trust the logic: If only one number fits, that's the answer — no second-guessing!
🏆 Why Naked Singles Matter
Naked Singles are the foundation of logical Sudoku solving:
- Easiest to spot — perfect for beginners building confidence
- 100% reliable — if you find one, it's guaranteed correct
- Creates chain reactions — solving one often reveals others
- Works at all difficulty levels — even expert puzzles have them
- Foundation for harder techniques — advanced methods build on this logic
🎓 Expert Insight
Even the world's best Sudoku solvers start every puzzle by scanning for Naked Singles. Combined with Hidden Singles, these two techniques can solve most easy and medium puzzles completely!
🎯 Ready to Practice?
Put your new knowledge to the test with our carefully crafted puzzle books. Start with Level 1 to build confidence with Naked Singles!
📚 Browse Our Sudoku Books📚 Continue Learning
Ready to expand your solving toolkit? Check out these related techniques:
- Hidden Single — The essential partner technique to Naked Single
- Naked Pair — When two cells share exactly two candidates
- Pointing Pairs — Using box/line interactions
- Box/Line Reduction — Advanced elimination technique