Sudoku Solving Techniques: A Complete Guide From Beginner to Advanced

1. Scanning (the foundation of every solve)

Scanning means picking a number, then checking every row, column, and box to see where it can and can't go. If a row already contains a 4, no other cell in that row can be a 4. The same rule applies to columns and to each box. Cross off the impossible cells in your head (or with pencil marks) and you'll often find a cell where only one number fits.

For example: say you're hunting for where 5 can go in a particular box. Two other cells in that box already share a row with a 5 elsewhere on the grid, and a third empty cell shares a column with another 5. That rules out three of the box's empty cells in one pass, often leaving just a single candidate cell for that 5.

On a 6x6 grid this alone will solve Easy and most Medium puzzles. On 9x9 grids, scanning gets you started but you'll usually need the next few techniques to finish.

2. Naked Singles

A "naked single" is a cell that has only one possible candidate left once you've eliminated every number already used in its row, column, and box. If you're keeping pencil marks (small candidate numbers in each cell), a naked single is any cell with just one pencil mark remaining — that number can be filled in immediately, no further checking required.

3. Hidden Singles

A hidden single is sneakier: a cell might have several candidates, but if it's the only cell in its row, column, or box that can hold a particular number, that number belongs there — even though the cell "looks" like it has other options. Instead of scanning cell by cell, try scanning number by number: for each digit 1 through 6 (or 1 through 9), find every box where it's missing and see if only one cell can take it.

For example, on a 9x9 grid, if 7 doesn't appear anywhere in a particular box yet, check each empty cell in that box: if six of them already rule out 7 because it appears in their row or column, and only one doesn't, that one cell must be 7 — even if it still shows three or four other pencil marks alongside it.

4. Naked Pairs

A naked pair is two cells in the same row, column, or box that share the exact same two candidates and nothing else. For example, if two cells in a row both show only "2, 7" as pencil marks, one of them must be 2 and the other 7 — you don't yet know which, but you know for certain that no other cell in that row can be a 2 or a 7. Removing those two candidates from the rest of the row often reveals a naked or hidden single elsewhere.

5. Hidden Pairs and Triples

A hidden pair is the mirror image of a naked pair: two candidates that only appear in two cells of a unit, even though those two cells still show other pencil marks alongside them. If 3 and 8 only appear as candidates in two cells of a box — no matter what else is pencilled into those cells — then 3 and 8 must occupy those two cells, so every other candidate can be erased from just those two.

Naked and hidden triples work the same way, just with three candidates spread across three cells instead of two. A naked triple is three cells in a unit whose combined candidates add up to only three distinct numbers — not every cell needs to show all three. A hidden triple is three numbers confined to only three cells in a unit. Triples show up less often than pairs, but they're worth checking whenever a unit still has three or more empty cells and pairs alone haven't cracked it.

6. Pointing Pairs and Box/Line Reduction

These two work across a box and a line, just in opposite directions. A pointing pair (or pointing triple) starts inside a box: if a candidate number only appears in two or three cells of a box, and those cells all sit in the same row or column, that number can be eliminated from the rest of that row or column outside the box — the box is "pointing" the candidate out along the line.

Box/line reduction runs the other way: if a candidate in a row or column only appears within a single box, it can be eliminated from the rest of that box's cells outside the row or column — the line is "claiming" the candidate for that box. Neither technique fills in a new digit by itself, but both often expose a naked or hidden single right afterward.

7. The X-Wing (for genuinely hard puzzles)

The X-Wing shows up on genuinely hard 9x9 puzzles, and occasionally on Hard Mini Sudoku too. Find a candidate number that appears in exactly two cells in each of two different rows — and those cells line up in the same two columns. That forms a rectangle: the number must occupy opposite corners of it, so you can eliminate it from every other cell in those two columns.

For example, if candidate 6 appears only in columns 2 and 7 within rows 1 and 4 — and nowhere else in either row — then any other 6 candidate in columns 2 or 7 outside rows 1 and 4 can be eliminated, because one of those four corners must hold every 6 those two rows need. It takes practice to spot, but it's one of the few techniques that reliably breaks puzzles that scanning and pairs alone can't crack.

8. Swordfish

A Swordfish is an X-Wing stretched across three rows instead of two. Find a candidate that appears in two or three cells across three different rows, with all of those cells confined to the same three columns. That's enough to prove the candidate must occupy exactly three of those nine intersections, so it can be eliminated from every other cell in those three columns (or rows, if you found the pattern by columns first). It's rare — most puzzles never need it — but when scanning, pairs, triples, and X-Wing have all stalled, a Swordfish is usually what's left to try.

9. Y-Wing (XY-Wing)

The Y-Wing uses three cells instead of a row/column pattern. Start with a "pivot" cell that has exactly two candidates, say X and Y. Find two other cells that each see the pivot (share a row, column, or box with it): one with candidates X and Z, the other with candidates Y and Z. Whichever of X or Y the pivot turns out to be, one of those two "pincer" cells is forced to be Z — so any cell that sees both pincer cells (whether or not it sees the pivot) can safely have Z eliminated as a candidate. It's the least visual technique here, but it's also the one that unlocks puzzles no line- or box-based technique can touch.

Which techniques do the variants need?

Every variant we offer builds on the techniques above rather than replacing them. For a full breakdown of how the variants differ, see our Mini vs Classic vs Killer vs Jigsaw vs Samurai comparison — but in short:

• • Mini Sudoku rarely needs more than scanning, singles, and naked pairs — the 6x6 grid runs out of cells before it needs much more.
• • Classic Sudoku is where pairs, triples, and pointing/box-line reduction start earning their keep, with the X-Wing showing up on the hardest puzzles.
• • Sudoku X and Jigsaw Sudoku use the exact same technique list as Classic — the extra work is remembering to check diagonals or region boundaries, not new logic.
• • Killer Sudoku adds cage-sum arithmetic on top of every technique above; you're still scanning and pairing, just with an extra constraint to satisfy.
• • Samurai Sudoku doesn't need anything new either — it just asks you to apply the same techniques across five overlapping grids at once.

Frequently asked questions

Practice makes it click

These techniques are cumulative — you don't need the X-Wing, Swordfish, or Y-Wing to enjoy Sudoku, and most puzzles never require them. The best way to internalize scanning, singles, and pairs is simply to play regularly. Our daily Mini Sudoku is a good low-pressure way to drill the basics in a few minutes, and Unlimited mode lets you practice a specific difficulty as many times as you like.