Sudoku FAQ — Everything You Need to Know
Quick answers to the most common Sudoku questions — rules, difficulty, techniques, printing, and how our website works.
The Basics
What is Sudoku?
Sudoku is a 9×9 logic puzzle. Fill the grid so every row, column, and 3×3 box contains 1–9 exactly once.
Is Sudoku a math game?
No. There’s no arithmetic. It’s logic and pattern recognition.
What are the basic Sudoku rules?
No duplicates: each row, each column, and each 3×3 box must contain the digits 1–9 exactly once. For a fuller explanation, see Sudoku rules.
Can a Sudoku have more than one solution?
A properly made Sudoku has exactly one solution. Multiple solutions usually means the puzzle is flawed.
Playing
How do I start a Sudoku puzzle?
Scan for easy wins: find a row, column, or box missing only one digit. Repeat the scan after each placement. A full walkthrough is on How to play Sudoku.
What should I do if I get stuck?
Rescan methodically. Add/update candidates (pencil marks), then look for singles or simple eliminations. If you still can’t progress, you may need a higher-level strategy.
Should I guess in Sudoku?
In general, no. Sudoku is meant to be solved with logic. If you’re guessing, you likely missed an elimination or need a new technique.
What does “notes mode” or “pencil marks” mean?
It’s a way to write small candidate digits in a cell, so you can eliminate possibilities without committing too early.
Strategies
What are the easiest Sudoku strategies?
Scanning + singles. Start with naked singles and hidden singles.
What is a naked single?
A cell that can only take one digit after you eliminate digits already used in its row, column, and box.
What is an X-Wing?
An advanced pattern that lets you eliminate a digit from other cells when it forms a 2×2 row/column alignment. See the full guide: X-Wing.
Our App & Website
Is Sudoku a Day free?
Yes. We keep the experience clean and calm, and we also publish free printable puzzle packs.
Where can I play a daily Sudoku?
Start here: Daily Sudoku. The iPhone app also includes a fresh daily puzzle.
How do Sudoku difficulty levels work?
Difficulty is about the solving techniques required and how deep the deductions are. Learn the levels here: Sudoku difficulty levels explained.
Printing
Where can I get printable Sudoku puzzles?
Download free weekly packs here: Printable Sudoku puzzles.
What paper size do the printable PDFs support?
Every level includes both A4 and US Letter versions.
Can I print just one Sudoku from a PDF pack?
Yes. The packs are multi-page PDFs — in your print dialog, select a single page (or a page range).
Still have a question?
If you’re deciding what to play next, these pages help: Easy, Hard, Expert, and difficulty levels.