Sudoku looks like a math puzzle, but there's no arithmetic involved — it's pure logic. If you can recognize the numbers 1 through 9, you can learn to solve it. Here's the method, built up one technique at a time.
The one rule that matters
A Sudoku grid is 9×9, divided into nine 3×3 boxes. The entire puzzle comes down to a single rule: every row, every column, and every 3×3 box must contain the numbers 1 through 9, with no repeats. That's it. Every technique below is just a smarter way of applying that one rule.
Start by scanning
The first and most useful technique is simple scanning. Pick a number — say, 5 — and look at where the 5s already appear. Because no row, column, or box can repeat a 5, each existing 5 "blocks" entire lines and boxes. Often you'll find a box where there's only one empty cell left that a 5 could legally go into. Place it, then move to the next number.
If two of the three rows passing through a box already contain a 7, then within that box, the 7 must go in the one remaining row — and often that leaves only a single possible cell.
Look for "single candidates"
Sometimes a particular empty cell can only hold one possible number, because the other eight already appear in its row, column, or box. These are called naked singles, and they're pure gifts. When the grid gets busy, scan individual empty cells and ask: of the numbers 1–9, how many are actually allowed here? When the answer is one, you've found a guaranteed placement.
Use pencil marks
Once the easy placements dry up, it's time to write small candidate numbers in the corners of empty cells — every value that could still legally go there. This feels tedious at first, but it transforms the puzzle. Patterns you couldn't see in your head become visible on the page.
With pencil marks in place, you can spot a cell where only one candidate remains, or a row where a particular number can only fit in one spot. The marks turn a guessing situation into a logic one.
A simple solving order
- Scan each number 1–9 and place every "obvious" one you can.
- When scanning stalls, fill empty cells with pencil-mark candidates.
- Hunt for cells with a single candidate and place them.
- Each placement removes candidates elsewhere — update and repeat.
- Keep cycling until the grid fills.
What not to do
Never guess. A proper Sudoku has exactly one solution reachable by logic alone, so if you find yourself flipping a coin between two numbers, you've simply missed a clue somewhere. Guessing leads to contradictions deep in the grid that force you to erase huge chunks of work. When you're stuck, the answer is to look harder, not to gamble.
When you're truly stuck
Everyone hits walls, especially on harder grids. The move is to slow down and re-scan the number you've used least — it often has untapped placements. Re-check your pencil marks for errors, since one wrong candidate poisons everything downstream. And if you just need one cell unstuck to get rolling again, a single targeted hint is far better than peeking at the whole solution.
Need a nudge, not the answer?
Our Sudoku Tools can give you a gentle single-cell hint, validate your progress, or solve the whole grid — your choice, no spoilers unless you want them.
Try the Sudoku Tools →Sudoku is a skill that compounds. The techniques that feel effortful today become automatic within a week or two, and puzzles you'd have called "hard" start to feel almost relaxing. Start with scanning, graduate to pencil marks, and trust the logic — it's always there.