How to solve Sudoku step by step, from your first grid to tricky ones

Sudoku looks like a maths puzzle, but you never add anything up. The digits 1 to 9 are just nine different symbols; they could be fruit or colors and the puzzle would work the same way. What you are really doing is ruling things out until only one answer is left in each square. Once that clicks, Sudoku stops feeling like guesswork and starts feeling like detective work.

The only rule

A Sudoku grid has nine rows, nine columns and nine 3 x 3 boxes. Some squares already hold a printed number. You fill the rest so that every row, every column and every box contains each of the numbers 1 to 9 exactly once. That is the whole game. Every technique below is just a different way of applying that single rule.

A well-made puzzle has exactly one solution and can be finished without guessing. If you ever feel forced to guess, it usually means a simpler step was missed somewhere, not that the puzzle needs luck.

Step 1: scan one number at a time

Beginners often stare at an empty square and ask "what goes here?" It is much faster to ask the opposite question: "where does the 7 go?"

Pick a number that already appears several times on the grid. Look at a box that does not have it yet. Every row and column that already holds that number is blocked for the whole box, so draw an imaginary line through them. Often only one square in the box survives, and the number must go there.

Work through all nine numbers this way, box by box. On an easy grid, this one technique can solve most of the puzzle on its own.

Step 2: finish nearly full lines

The second easy win is the line with only one or two gaps. If a row already holds eight different numbers, the missing ninth is obvious. With two gaps, check which of the two missing numbers already appears in each gap's column or box; usually one of them is blocked, and both squares fill at once.

Scanning and finishing lines feed each other. Every number you write gives the next scan more to work with, so keep switching between the two.

Step 3: use notes when the easy moves run out

Sooner or later, scanning stops producing answers. This is where pencil marks, also called notes or candidates, come in. For a crowded area of the grid, write the small numbers that could still go in each square.

You do not need to note every square on the board. Start with one box or one row that is mostly full. Notes turn a vague feeling into a list you can check, and they reveal the next two techniques, which are almost impossible to spot without them.

In our Sudoku, turn on Notes with the button under the grid (or press N) and tap numbers to pencil them in. When you later write a number in ink, the game clears that number from the notes in the same row, column and box for you.

Step 4: spot pairs

Imagine two squares in the same row whose notes both say only "3 or 8". You do not know which is which yet, but you know those two squares will use up the 3 and the 8 between them. So no other square in that row can be a 3 or an 8. Cross those numbers out of every other note in the row, and something new often falls into place.

The same works for a column or a box, and for three squares sharing three numbers. Hunting for pairs is the single biggest step up from easy to medium puzzles.

Step 5: pointing numbers

Sometimes, inside one box, a number can only go in squares that all sit in the same row. The box will use that number somewhere along that row, which means the rest of the row, outside the box, cannot have it. This is called a pointing pair, and it is a quiet but powerful way to remove notes.

When you get stuck

Being stuck is normal. Try these in order:

1. Run the number scan again from 1 to 9. A number written ten moves ago may have unlocked something.
2. Look for a row, column or box with only two or three gaps.
3. Check your notes for pairs you have not used yet.
4. Take a short break. Fresh eyes spot what tired eyes skip.

If you are still stuck, a hint that explains the next step is better than a guess. The hint in our Sudoku game names the technique it used, so you learn the move instead of just copying a number.

A gentle way to practise

If a full 9 x 9 grid feels like a lot, start smaller. Mini Sudoku uses the same rule on four by four and six by six boards, with colored lanterns that make patterns easy to see. When you want arithmetic on top of the logic, Math Sudoku adds sums and products to each cage. The core habit, ruling out before filling in, is the same in all three.

Start with an easy grid, use scanning until it stops working, then reach for notes. After a handful of puzzles, the steps above become automatic, and that is exactly when Sudoku becomes fun.