Naked Singles in Sudoku: Step-by-Step with Interactive Examples

Naked Singles are the fastest reliable wins in Sudoku. If one cell has only one valid number left, place it immediately — no guessing.

This guide gives you a practical workflow, quick safety checks, and interactive examples that match each stage of solving.

What Is a Naked Single?

A naked single occurs when an empty cell has only one possible number left after eliminating every digit already placed in its row, column, and 3×3 box. Because all other candidates are ruled out, that one remaining digit is the confirmed answer — place it immediately.

• If one candidate remains: place it.
• If two or more remain: keep scanning and do not place yet.

Mastering this one rule gives you a dependable base for Hidden Singles, Naked Pairs, and later techniques like X-Wing.

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When to Use Naked Singles

Use Naked Singles continuously throughout a puzzle, especially:

• right after filling obvious givens,
• after every correct placement,
• and whenever progress slows down.

Simple habit: after each move, do one quick naked-single scan before trying anything advanced.

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A 5-Step Spotting Workflow

1. Scan one 3×3 box. Keep your order fixed (top-left to bottom-right).
2. Check each empty cell. Eliminate digits already present in row, column, and box.
3. Keep only valid candidates. Do not guess between options.
4. Place immediate singles. If one candidate remains, place it right away.
5. Repeat in the same area first. New singles often appear instantly.

Example A · Easy confidence pass

Find cells with exactly one valid candidate and place them before moving on.

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Quick Checks Before You Place

Before writing a number, run this 3-point safety check:

• Does this number already exist in the row?
• Does this number already exist in the column?
• Does this number already exist in the 3×3 box?

If any answer is yes, it is not a valid naked single.

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Common Mistakes (and Fast Fixes)

1) Rushing without checking all 3 constraints

Fix: always validate row, column, then box — in the same order every time.

2) Scanning randomly

Fix: use a fixed loop so you skip fewer easy placements.

3) Treating two-candidate cells as solved

Fix: only place a number when one candidate remains.

Example B · Mixed board with distractions

Some cells look easy but still have two candidates. Place only true singles.

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Naked Single vs Hidden Single

• Naked Single: one cell has one candidate.
• Hidden Single: one digit has one possible location in a row, column, or box.

Run naked-single checks first. Then run hidden-single checks for the next layer of progress.

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Bridge to Your Next Strategy

After clearing all available naked singles, the puzzle shifts naturally into hidden singles territory. Naked singles and hidden singles work as a pair — naked singles clear the explicit slots, hidden singles find the hidden ones — and together they resolve most beginner and intermediate puzzles. Once both singles techniques are exhausted, the typical next step is Naked Pairs, followed by Pointing Pairs for box-based eliminations.

Example C · Bridge to next technique

Complete all Naked Singles first, then continue with Hidden Singles for the next breakthroughs.

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Practice Naked Singles

Easy puzzles are the ideal starting point — they contain enough naked singles to confirm your scanning order is working. Once they feel automatic, step up to medium puzzles where naked singles and hidden singles appear together.

• Today's free daily Sudoku — a new puzzle every day, great for a focused naked-singles scan
• Printable Easy Sudoku PDFs — take a few offline and practice the systematic box-by-box pass

Once naked singles feel reliable, move on to Hidden Singles — they follow directly from the same scanning habit but require looking across a whole unit instead of at a single cell.

What to Study Next

Naked Singles sit at the base of every Sudoku solver's toolkit. Browse the full progression in our complete strategy guide.

• Hidden Singles — the immediate follow-on technique; same elimination logic extended to a whole row, column, or box instead of a single cell
• Pencil Marks Strategy — a systematic way to track candidates that makes naked singles, hidden singles, and pair techniques faster and more reliable
• Naked Pairs — the natural step up once naked and hidden singles stop being enough; uses the same candidate-elimination thinking across two cells at once
• Naked Triples — extends the naked-family logic to three cells; the next milestone in the same progression path
• Pointing Pairs — a box-alignment elimination technique that comes into play once singles no longer yield new placements

← Back to All Strategies

Frequently Asked Questions

Ready to put it into practice? Try today's daily Sudoku. When naked singles alone aren't enough to finish the puzzle, that's your cue to move on to Hidden Singles.