How to Solve Sudoku: A Beginner Guide That Actually Works

Short answer: Solve Sudoku by scanning rows, columns and boxes for cells where only one number can legally go. Every valid Sudoku is solvable by pure logic — you never need to guess. Start with the number that appears most often on the grid. Practise on a quick 4×4 Sudoku before moving to full 9×9 grids.

The one rule

Each row, each column and each box must contain every digit exactly once. In a 9×9 grid that is 1–9; in a 4×4 grid it is 1–4. That single rule generates everything else.

The mistake beginners make is treating this as a maths puzzle. There is no arithmetic in Sudoku. The digits could be letters or colours and nothing would change. It is a constraint puzzle.

Technique 1: Scanning (solves most easy puzzles on its own)

Pick a digit — start with whichever already appears most often. Say it is 5.

1. Find every 5 already on the grid.
2. Mentally draw a line through each row and column containing a 5.
3. Look at a box with no 5 yet. Those lines eliminate most cells.
4. If exactly one cell survives, that is where the 5 goes.

Work through all nine digits this way. On an easy puzzle you will often finish without needing anything else. This technique is sometimes called cross-hatching, and it is the single highest-value thing to learn.

Technique 2: The last empty cell

Whenever a row, column or box has eight of its nine cells filled, the last one is forced. Obvious, but easy to miss — always rescan the lines around a cell you just filled, because filling one cell often unlocks two or three others in a chain.

Technique 3: Pencil marks

When scanning stops producing answers, write small candidate numbers in each empty cell — every digit that could legally go there. This is where most people start making real progress on medium puzzles.

Two things fall out immediately:

• Naked single — a cell with only one candidate. Fill it in.
• Hidden single — a digit that appears as a candidate in only one cell of a row, column or box. Even if that cell has several candidates, the digit has nowhere else to go.

Hidden singles are the technique that separates people who finish medium puzzles from people who stall on them. They are easy to miss because the cell looks ambiguous until you check the whole line.

Technique 4: Naked pairs

If two cells in the same row, column or box have exactly the same two candidates — say both can only be 3 or 7 — then those two digits are locked into those two cells. You do not know which goes where, but you know no other cell in that line can be 3 or 7. Remove them as candidates everywhere else in that line.

This usually cascades. One naked pair often creates a naked single somewhere nearby.

Technique 5: Pointing pairs

If all the candidates for a digit within one box sit in the same row, that digit must be in that row somewhere inside the box — so it can be eliminated from the rest of that row outside the box. The same works for columns.

Slightly harder to spot, but it breaks open most hard puzzles.

The order to apply them

Efficiency matters more than knowing exotic techniques. Work in this order and only escalate when you are stuck:

1. Scan for each digit (cross-hatching)
2. Fill any obvious last-cell-in-a-line
3. Add pencil marks
4. Naked singles, then hidden singles
5. Naked pairs
6. Pointing pairs

Return to step 1 every time you fill a few cells. New information changes what scanning can find, and people forget to go back.

Mistakes that keep beginners stuck

• Guessing. A valid Sudoku never requires it. If you are guessing, you have missed something — and one wrong guess corrupts the whole grid in a way that is painful to unwind.
• Not updating pencil marks. Stale candidates cause more errors than anything else. Every time you place a digit, clear it from the candidates in that row, column and box.
• Fixating on one region. If a box will not yield, leave it. The information you need is usually elsewhere.
• Treating it as arithmetic. Adding up rows is not a Sudoku technique.

How long should it take?

For a 9×9: easy puzzles 5–10 minutes, medium 10–20, hard 20–45. Experienced solvers finish easy grids in under three minutes, mostly by scanning faster rather than by knowing more techniques.

If you are new, start with the 4×4 Sudoku. Same logic, one-quarter the grid, and it teaches scanning without the intimidation.

Why Sudoku is worth playing

It trains systematic elimination — working out what something must be by ruling out what it cannot be. That is a genuinely transferable habit of thought, which is more than can be said for most puzzle games.

If you enjoy this style of thinking, try Number Sequence for pattern logic and Box Memory for working memory.

Related reading: number sequence puzzles with answers.