FAQ

Common questions about Sudoku, answered clearly and directly.

Getting Started

Do I need to be good at math to play Sudoku?

No. Despite using numbers, Sudoku is a logic puzzle, not a math puzzle.

You never add, subtract, multiply, or divide. The digits 1-9 are just symbols — you could replace them with letters A-I or shapes and the puzzle would work identically.

The skill is pattern recognition and logical deduction, not arithmetic.

How do I know if my puzzle has an error?

Signs of an error:

• A row, column, or box has the same digit twice
• A cell has no possible candidates
• You've "solved" the puzzle but something doesn't fit

What to do:

• Check recent placements
• Use your app's error-checking feature if available
• Consider undoing back to a known-good state

Is it cheating to use hints?

That depends on your goals.

• Learning: Hints are valuable teachers. Use them.
• Casual play: Your game, your rules.
• Timed competition: Hints would defeat the purpose.
• Building skills: Try without hints first, use them when truly stuck.

There's no Sudoku police. Use hints if they help you enjoy the game.

What's the best difficulty to start with?

Start with Easy puzzles. Seriously.

Even if you consider yourself smart, Easy puzzles teach:

• The rules and interface
• Basic scanning techniques
• What "solved" feels like

Once Easy feels trivial, move to Medium. There's no shame in gradual progression.

Solving Questions

I'm stuck and can't find any moves. What should I do?

In order, try:

1. Re-scan for naked singles — check every empty cell
2. Look for hidden singles — where can each digit go in each unit?
3. Verify your notes — one wrong note derails everything
4. Try a different region — fresh eyes on a new area
5. Take a break — seriously, 5-10 minutes helps
6. Use a hint — learn what you missed

See the "When You're Stuck" guide for detailed strategies.

Should I use notes (pencil marks)?

It depends on difficulty:

Notes aren't required, but they become increasingly valuable as puzzles get harder. There's no "right" answer — some expert solvers use minimal notes, others use full candidate notation.

How long should a puzzle take?

There's no "should." Times vary wildly by:

• Puzzle difficulty
• Your experience level
• Whether you're rushing or relaxing

Rough benchmarks for practiced solvers:

• Easy: 2-5 minutes
• Medium: 5-15 minutes
• Hard: 10-30 minutes
• Expert: 20-60+ minutes

But these are just reference points. Solve at whatever pace you enjoy.

Can a puzzle have more than one solution?

Properly constructed Sudoku puzzles have exactly one solution.

If you find two valid solutions, either:

• The puzzle is poorly made
• You've made an error somewhere

Quality puzzle sources ensure unique solutions.

Is it ever necessary to guess?

For properly constructed puzzles: No.

Every valid Sudoku can be solved through pure logic. However:

• Some puzzles require very advanced techniques
• If you don't know those techniques, it may feel like guessing is necessary
• "Bifurcation" (trying a value to see if it leads to contradiction) is a valid technique, though purists avoid it

If you find yourself guessing regularly:

• Your technique knowledge may have gaps
• The puzzles may be beyond your current level
• Consider easier puzzles or learning new techniques

Rules Clarifications

What exactly is a "box"?

The 3×3 outlined regions in the grid. There are 9 boxes total.

Box 1 | Box 2 | Box 3
------+-------+------
Box 4 | Box 5 | Box 6
------+-------+------
Box 7 | Box 8 | Box 9

Each box must contain digits 1-9 with no repeats, just like rows and columns.

Can the same digit appear in a diagonal?

In standard Sudoku: Yes.

The diagonals have no special rules. The same digit can appear multiple times along a diagonal.

In Diagonal Sudoku (variant): No. Both main diagonals must also contain 1-9 without repeats.

Do the given (starting) numbers follow a pattern?

In quality puzzles:

• Given digits are typically symmetric (rotational or reflective)
• This is aesthetic preference, not a rule
• Some modern puzzles intentionally break symmetry

For solving: The pattern of givens doesn't help you solve — treat each puzzle fresh.

Technical Questions

Why are some puzzles rated "Evil" or "Diabolic"?

Puzzle rating systems estimate difficulty based on:

• Number of given digits (fewer = generally harder)
• Techniques required to solve
• How "deep" the required logic goes

Common rating scales:

• Easy → Medium → Hard → Expert → Master → Evil
• 1-5 stars
• Numerical ratings

Different apps use different scales. An "Expert" puzzle in one app might equal "Hard" in another.

How are Sudoku puzzles created?

Two main methods:

Computer generation:

• Algorithms create valid grids
• Digits are removed while ensuring unique solution
• Quality varies — some are elegant, others mechanical

Human construction:

• Puzzle designers craft puzzles by hand
• Often more elegant solving paths
• Can be designed around specific techniques

Both methods can produce quality puzzles.

Is there a maximum/minimum number of given digits?

Minimum for unique solution: 17 given digits

• Mathematically proven (2012)
• 17-clue puzzles exist but are extremely hard
• Most puzzles have 22-30 givens

Maximum: Technically, you could give 80 of 81 cells, but that's not much of a puzzle. Practical puzzles rarely exceed 35-40 givens.

Improvement Questions

How do I get faster?

Speed comes from:

1. Pattern recognition — seeing solutions without conscious analysis
2. Technique mastery — knowing what to look for
3. Interface fluency — fast input without thought
4. Consistent practice — daily solving builds speed

See the "Speed Solving" guide for detailed strategies.

What techniques should I learn next?

Typical progression:

1. Foundation: Naked singles, hidden singles, scanning
2. Intermediate: Naked/hidden pairs, pointing pairs, box/line reduction
3. Advanced: X-Wing, XY-Wing, simple coloring
4. Expert: Swordfish, chains, unique rectangles

Don't skip levels. Each technique builds on previous understanding.

How can I track my improvement?

Metrics to track:

• Average solving time by difficulty
• Success rate (completed without errors)
• Techniques used
• Puzzles where you got stuck

Good signs of improvement:

• Faster times
• Fewer errors
• Less time stuck
• Easier recognition of patterns

Misc Questions

Is Sudoku good for my brain?

Sudoku provides:

• Pattern recognition practice
• Logical thinking exercise
• Focus and concentration training
• Meditative, stress-reducing activity

Sudoku is not proven to:

• Prevent dementia (despite marketing claims)
• Increase IQ
• Transfer to non-puzzle skills

Enjoy it for what it is: a satisfying mental exercise.

Why do I sometimes see "数独" instead of "Sudoku"?

That's the Japanese kanji for Sudoku:

• 数 (sū) = number
• 独 (doku) = single

The name means approximately "single numbers" or "numbers must be single."

Where does the word "Sudoku" come from?

Japanese puzzle company Nikoli shortened "Sūji wa dokushin ni kagiru" (数字は独身に限る) — meaning "the digits must be single."

"Sudoku" is the abbreviated form that became the worldwide standard.

Are there Sudoku tournaments I can enter?

Yes!

• Online: Logic Masters platforms, app leaderboards, regular online contests
• Local: Puzzle clubs, library events, local championships
• National: Many countries have national championships
• International: World Sudoku Championship

See the "Competitive Sudoku" guide for details.

I finished a puzzle but it says I have errors. What happened?

Possibilities:

• A digit appears twice in a row, column, or box
• The solution doesn't match the given digits
• Your app's solution-checking may differ from the intended solution (rare)

To diagnose:

• Look for highlighted conflicts
• Check each unit systematically
• Trace back to find where the error started