Sudoku for Beginners: 5 Simple Rules to Get Started
Sudoku Series: Hub · Beginner · Intermediate · Advanced
Sudoku looks hard when you first see it — nine rows, nine columns, eighty-one cells. But here is the truth: Sudoku is not a math puzzle. You never add or subtract anything. You just use simple logic, one step at a time.
These five rules are enough to solve every easy Sudoku and make real progress on medium ones.
What You Need to Know First
A Sudoku grid is 9×9, split into nine 3×3 boxes. Some cells come pre-filled. You fill the rest.
The only rule: Every row, every column, and every 3×3 box must have each digit from 1 to 9 exactly once.
That is the whole game. The five rules below show you how to use that one rule to solve puzzles.
Rule 1: Look Before You Write (Scan and Cross-Hatch)
Spend 60 seconds scanning the grid before you fill anything in. Look for:
- Rows, columns, or boxes with only one or two empty cells. You can almost always solve these right away.
- Digits that appear 7 or 8 times. A digit that appears 8 times needs only one more placement — you can find it by elimination.
New solvers rush to fill cells. Experienced solvers scan first and collect easy placements that make the rest of the puzzle simpler.
Example: Digit 3 appears elsewhere in the grid (at R1C7, R3C8, R6C1, R8C3), but the top-left box (rows 1–3, columns 1–3) has no 3 yet. Cross-hatch: row 1 already has a 3 → ruled out. Row 3 already has a 3 → ruled out. Column 1 already has a 3 → ruled out. Column 3 already has a 3 → ruled out. The only surviving cell in the top-left box is R2C2. Place 3 there.
Cross-hatching is the systematic version of this scan. Pick a digit that appears 7 or 8 times. Go box by box through every box that does not yet have it. In each box, mark which empty cells cannot hold the digit (any cell whose row or column already has it). If only one cell remains in a box, fill it. This is the beginner’s single most powerful scanning tool.
Rule 2: Use the One-Digit Rule (Naked Singles)
A naked single is a cell where only one digit can go. Every other digit from 1–9 already appears in that cell’s row, column, or box.
How to find one:
- Pick any empty cell.
- Look at its row — which digits are there?
- Look at its column — which digits are there?
- Look at its 3×3 box — which digits are there?
- Cross off every digit you see. Whatever is left is your answer.
Example — three layers of elimination:
Watch the animation: cell R5C5 is penciled with all nine candidates (1–9). Neighbors eliminate them one by one:
- Row 5: contains 1 (C1), 7 (C7), and 3 (C9) → eliminate 1, 3, 7
- Column 5: contains 4 (R1) and 9 (R9) → eliminate 4, 9
- Center box (rows 4–6, cols 4–6): contains 2 (R4C4), 6 (R6C6), and 8 (R6C4) → eliminate 2, 6, 8
That rules out all eight other digits. The only candidate left is 5. Write it in.
Easy puzzles can usually be solved entirely by finding naked singles. Try any “easy” rated Sudoku and look for cells where many neighbors are already filled.
Rule 3: Look for Hidden Singles
A hidden single is a digit that has only one valid cell in a row, column, or box — even if that cell looks like it has multiple options.
How to find one:
Pick a digit (say, 5). Go box by box. For each box that does not yet have a 5, check which empty cells can hold a 5. A cell cannot hold 5 if 5 already appears in its row or column.
If only one empty cell remains in a box, place 5 there.
Example — digit 5 in the bottom-center box (rows 7–9, columns 4–6):
The box has empty cells at R7C4, R7C5, R8C4, R8C6, and R9C5 (the other four cells are already filled).
- Row 7 already has a 5 (column 2) → R7C4 and R7C5 are blocked.
- Column 4 already has a 5 (row 3) → R8C4 is blocked.
- Column 6 already has a 5 (row 5) → R8C6 is blocked.
Only R9C5 has no 5 in its row or column. Place 5 there.
Hidden singles are where most beginners get stuck. Once you train yourself to ask “where can this digit go?” for every box, medium puzzles open up quickly.
Rule 4: Never Guess — Eliminate Instead
Guessing is the enemy of Sudoku. If you guess wrong, you may not find the mistake until ten moves later.
Instead, eliminate. When a cell seems to have too many options, use the three checks from Rule 2: row, column, box. You will almost always find you can cross off enough candidates to force an answer — or at least narrow things down for the next pass.
The core loop: Scan → Cross-hatch → Naked single → Hidden single → Repeat.
Rule 5: Update as You Go
Every time you place a digit, that digit affects every empty cell in its row, column, and box. New naked singles appear.
After each placement:
- Glance at the row — any naked singles?
- Glance at the column — same check.
- Glance at the 3×3 box — same check.
One correct placement on a beginner puzzle can trigger ten more. This is what makes Sudoku satisfying — the logic accelerates.
Your First Solving Loop
- Scan the grid for digits appearing 7–8 times. Place any you can find right away.
- Check for naked singles — look at every empty cell, see if only one digit fits.
- Check for hidden singles — for each digit 1–9, check each row, column, and box to see if there is only one valid cell.
- After each placement, re-check the row, column, and box for new naked singles.
- Repeat until solved.
On an easy puzzle, this loop completes the grid. On medium, you may need pencilmarks and a couple of extra techniques — see the complete Sudoku guide for those.
Recap Checklist
After working through these five rules, you should be able to:
- Spend 60 seconds scanning before writing anything — find digits that appear 7 or 8 times, and rows/columns/boxes with one or two empty cells.
- Use cross-hatching: track a digit box by box, eliminate cells blocked by row and column, and place it when only one cell remains.
- Find a naked single: pick an empty cell, check its row, column, and box, and place the one digit that is not already present.
- Find a hidden single: for each digit 1–9, check each box for a cell where only one empty cell can hold it.
- Never guess — every placement should be provably correct from what you can see.
- After each placement, immediately scan its row, column, and box for new naked singles.
Frequently Asked Questions
Q: Do I need to be good at math?
No. Sudoku uses the digits 1–9 as symbols, not numbers. You never calculate anything — you just check whether a digit already exists somewhere. You could replace 1–9 with letters and the puzzle would work the same way.
Q: How long should a beginner puzzle take?
Easy puzzles typically take 10–20 minutes for a first-time solver. With practice that drops to 5–8 minutes. Speed is not the point — accuracy is.
Q: What is the difference between easy, medium, and hard Sudoku?
Difficulty depends on which techniques you need. Easy: naked singles and basic scanning. Medium: adds hidden singles and cross-hatching. Hard: needs naked/hidden pairs and pointing pairs. Expert adds X-Wing and harder patterns.
Q: Should I use pencilmarks?
For easy puzzles, no — you can spot naked singles by eye. Once you reach medium difficulty, pencilmarks (small candidate digits in each cell) become essential. They turn the puzzle from a memory task into a visible logic exercise.
Q: Can every Sudoku be solved without guessing?
Yes. Every well-made Sudoku is designed for pure logic. If you feel you have to guess, you have missed a technique.
What to Try Next
- Sudoku Series Hub — Full technique overview and level chooser.
- Intermediate: Naked Pairs, Pointing Pairs, Box-Line Reduction — The next step when easy puzzles are no longer a challenge.
- Naked Singles and Hidden Singles: Sudoku’s Foundation — Deepen your mastery of the two most important beginner techniques.
- The X-Wing Technique Explained — When you are ready for the first real advanced technique.
- How to Solve Logic Grid Puzzles — Deduction puzzles that use a similar elimination mindset.
- Nonogram for Beginners: 5 Simple Rules to Get Started — The same logic-first mindset, applied to picture-cross puzzles.
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