Sudoku for Beginners: The Four Techniques That Solve Most Puzzles

Sudoku has exactly one rule: every row, every column and every three-by-three box contains the digits 1 to 9 once each. That is the whole game. Everything else is technique for finding where the digits go.

Beginners usually stall not because the puzzles are hard but because they are looking at the grid the wrong way — hunting for empty cells and asking "what goes here?" That question is slow. The faster question is "where does this number go?", and it is the basis of everything below.

Four techniques will solve almost every easy and medium puzzle you meet. They are worth learning in order, because each one picks up where the last runs out.

1. Scanning: pick a number and hunt it

This is the technique to use first, every time, and the one that does most of the work.

Choose a digit — say 5. Look at the grid and find the boxes that do not contain a 5 yet. For each of those, look along the rows and columns that pass through it. Every row that already has a 5 eliminates three cells in that box. Every column with a 5 eliminates three more.

Often you will find a box where those eliminations leave exactly one empty cell where the 5 can go. Place it. Then keep going with the same digit across the rest of the grid, because placing one 5 creates new eliminations for the others.

Work through the digits one at a time, and do the whole grid for each. On an easy puzzle, scanning alone will fill most of the board. The reason it is so efficient is that you are holding one number in your head instead of nine.

2. Naked singles: the cell with one option left

Where scanning asks "where does this number go?", this asks the opposite: "what can go in this cell?"

Look at an empty cell and list what is excluded — every digit already present in its row, its column, or its box. If eight digits are excluded, the ninth is forced. Place it.

This is called a naked single, and it becomes common in the mid-game, after scanning has filled enough of the grid to constrain individual cells. The practical trick is knowing where to look: cells in a busy intersection — a nearly-complete row crossing a nearly-complete column inside a nearly-complete box — are where naked singles hide. Cells in an empty corner of a sparse grid almost never are.

3. Hidden singles: the number with one home left

This one catches beginners out, and it is the technique that unlocks medium puzzles.

Look at a single region — one row, one column, or one box — and pick a digit missing from it. Check each empty cell in that region and ask whether that digit could legally go there. If there is exactly one cell where it can, it goes there, even if that cell has several other candidates.

That last part is what makes it "hidden". The cell might look wide open, with four possible values. But if this region has nowhere else to put its 7, the cell is a 7, and the other candidates are irrelevant.

Beginners miss hidden singles because they are looking at cells rather than regions. When a puzzle stalls and no cell obviously has one option, switch to examining regions and asking where each missing digit can still live.

4. Pointing pairs: eliminating without placing

The first technique that does not place a number, and the bridge into harder puzzles.

Suppose in one box, a digit — say 4 — can only go in two cells, and both are in the same row. You do not know which of the two is the 4, but you know the box's 4 is somewhere in that row. Therefore no other cell in that row, outside the box, can be a 4.

That elimination usually does not solve anything by itself. It removes candidates elsewhere, and the removal creates a naked single or a hidden single somewhere across the grid. The same logic works with columns, and in reverse: if a digit in a row can only appear inside one box, it can be eliminated from the rest of that box.

This is the point where writing candidates down starts paying for itself. Which brings us to the practical question.

Should you write pencil marks?

For easy puzzles, no. Marking candidates in every cell takes longer than scanning and makes the grid noisy.

For medium and hard puzzles, yes, but selectively. Mark candidates in a region you are actively working, not across the whole board. Most digital sudoku has a notes mode for this, and some will auto-fill candidates — useful for learning where they come from, but it removes the elimination practice that makes you faster later.

Getting unstuck

When a puzzle stops moving, run this in order:

1. Re-scan every digit 1 to 9 across the whole grid. You almost certainly missed a placement — this is the most common cause of being stuck.
2. Check each region for hidden singles, region by region rather than cell by cell.
3. Look for pointing pairs in boxes where a digit has only two or three possible positions.
4. If none of that moves it, the puzzle needs a harder technique than these four — which is a reason to check the difficulty setting, not a reason to guess.

Never guess. A guess in sudoku either does nothing or corrupts the grid in a way you will not notice for ten minutes. If it seems like guessing is required, something earlier was missed.

Practising properly

Difficulty ratings are the useful tool here. Play at a level where you stall occasionally but finish most of the time. Easy puzzles you complete without pausing build speed but not skill; puzzles you cannot finish build frustration.

We built Action Sudoku with five difficulty tiers for exactly that reason, plus a daily challenge with a streak if you want the habit rather than the marathon. Solo puzzles work offline. When you are quick enough that a solo puzzle feels routine, the real-time 1v1 mode is a decent shock to the system — the techniques are the same, but you have to run them under time pressure against someone doing the same.

If you want to work on speed specifically rather than technique, that is a different problem with a different answer: see how to get faster at sudoku.

All articles