The Rules (Simple Once You Know Them)

A sudoku puzzle is a 9x9 grid divided into nine 3x3 boxes. Some cells are pre-filled with numbers. Your job is to fill in the rest so that:

  • Every row contains the numbers 1–9 exactly once
  • Every column contains the numbers 1–9 exactly once
  • Every 3x3 box contains the numbers 1–9 exactly once

That is the entire ruleset. No maths required — the numbers could be replaced with letters or symbols and the puzzle would work identically. It is purely about logic.

Strategy 1: Scanning (Start Here)

  1. 1

    Find rows, columns or boxes with only one missing number

    If a row already has 1,2,3,4,5,6,7,9 filled in, the empty cell must be 8. Find these easy wins first and fill them in.

  2. 2

    Focus on numbers that appear most in the puzzle

    Pick a number that already appears many times in the grid — say there are seven 7s already placed. Only two 7s are missing. Scan each row, column and box: two rows do not have a 7 yet. Which cells in those rows can a 7 go? Eliminate any cell already in a column or box that has a 7. Often only one cell remains.

Strategy 2: Elimination

  1. 3

    For each empty cell, list what numbers are possible

    Look at the row, column and 3x3 box the empty cell belongs to. Any number that already appears in any of those three cannot go in that cell. If only one number is possible — fill it in. This is called the "sole candidate" technique.

  2. 4

    Use pencil marks for harder puzzles

    Write small possible numbers lightly in each cell. As you fill in other cells, cross off pencil marks that are no longer possible. This is called "candidate notation" and is essential for medium and hard puzzles.

Strategy 3: Naked Pairs

If two cells in the same row/column/box each contain only the same two possible numbers (e.g. both show 3 and 7), those two numbers must go in those two cells — in some order. You can eliminate 3 and 7 as possibilities from all other cells in that row/column/box. This advanced technique unlocks many stuck puzzles.

Never guess on easy or medium puzzlesGenuine sudoku puzzles have exactly one solution reachable through pure logic — no guessing needed. If you are guessing, return to elimination and look more carefully. Harder puzzles may require more advanced techniques like X-wings or Swordfish, but beginner and intermediate puzzles are always solvable by elimination alone.

Frequently Asked Questions

Easy puzzles: 5–15 minutes for beginners, under 5 minutes once experienced. Medium: 15–30 minutes. Hard: 30–60+ minutes. Expert/extreme: can take hours. Time varies enormously between individuals — consistency of practice matters more than speed.
Sudoku exercises logical thinking, pattern recognition and concentration. Research suggests regular puzzle-solving may help maintain cognitive function with age. Like any mental exercise, it is beneficial as part of a varied mentally stimulating lifestyle — though not a standalone brain training solution.