Every sudoku can be solved without guessing — if you know where to look. On this page you'll learn the five techniques that take you from easy to hard, in plain language and without secret jargon. Don't know the rules yet? Then first read the rules of sudoku.
The order below is also the best order to learn them in. The first two are enough for easy puzzles; if you master all five, you'll solve hard grids too.
The simplest technique, and where every puzzle begins. Pick a digit that already appears often in the grid — the 5, for example — and go along the three boxes of a row. Is there already a 5 in two of the three boxes? Then the 5 of the third box must be in the remaining row. Often only one cell is left. Work through all the digits from 1 through 9 this way and you'll fill in the first cells effortlessly.
Look at one empty cell and cross off everything that's no longer possible: the digits already in the same row, column, and box. Is exactly one digit left? Then that's called a naked single and you can fill it in with certainty. In easy puzzles this alone takes you a very long way.
This is the reverse way of thinking. Instead of looking at one cell, you look at one digit within a row, column, or box: in which places can the 7 still go here? If there is only one cell where the 7 doesn't clash with another 7 — even if at first sight more digits would fit in that cell — then the 7 must go there. It was “hidden” among other possibilities, hence the name.
When the puzzle grinds to a halt, it's time for pencil work: note in every empty cell, in small print, which digits are still possible (“candidates”). On paper you do that in the corners of the cell; on BreinPlezier you simply use notes mode. As soon as you fill in a digit somewhere, cross it off in the neighboring cells. Cells with only one candidate left practically fill themselves in.
A step further, for medium and hard puzzles. Can all candidates for a digit within one box only lie on the same row (or column)? Then that digit is certainly on that line in that box — and you may cross the digit off in the rest of that row or column, even outside the box. That's how one discovery makes the next one possible.
Practice a new technique on puzzles you find easy. That way you learn to recognize the pattern without the pressure of a hard grid.
Choose your levelSolve a whole puzzle using only scanning and naked singles. Only when that goes smoothly do you add the next technique.
Daily puzzlePracticing pencil marks is wonderfully old-fashioned on paper. Print a bundle of puzzles with solutions to check your work.
Print sudokuMeanwhile, avoid the pitfalls: we describe the common mistakes in sudoku alongside the rules.
No. Every good sudoku — and every puzzle on BreinPlezier — can be solved entirely by logical reasoning. If you're stuck, there is always a naked single or hidden single to be found somewhere. Guessing actually breaks the puzzle: one wrong digit works its way through the whole grid.
Start with scanning and naked singles: with those you can solve easy puzzles completely. Then add hidden singles for the medium level, and pencil marks plus box interaction for hard puzzles.
Small helper digits you note in an empty cell to keep track of which digits are still possible there. On paper you write them small in the corners; in the online puzzle on BreinPlezier you turn them on with notes mode.
Hard puzzles have fewer filled-in cells, so scanning alone isn't enough. The secret is working systematically: note candidates, look for hidden singles, and use box interaction. And feel free to take a break — with fresh eyes you often spot at a glance what you missed before.
Certainly, sudoku with pen and paper works exactly the same. Print free puzzles at your level — with a solution sheet to check your work — via our print page.