Medium Sudoku
Medium sudoku is the bridge tier. Scanning and singles still do most of the work, but every puzzle here contains at least one moment where no cell can be filled directly. You break those moments with candidates: the small digits that track what each cell could still be.
If you can clear our easy puzzles without slowing down, this page is your next step.
What makes a puzzle medium
We grade puzzles by the hardest technique they force, and a medium puzzle forces at least one move beyond singles: locked candidates or a naked pair. Our solver verifies this for every puzzle before it ships, and it also verifies the other direction. Nothing on this page requires the hidden pairs, triples or X-wings that define hard sudoku.
So a medium stall is a specific kind of problem with a specific kind of answer, and both techniques you need are below.
Pencil marks that earn their keep
Tap the pencil icon (or press N) and your digits become notes. Tap a candidate again to remove it. The button fills in while note mode is on:
You do not need marks in every cell; write them only where the puzzle has gone quiet, usually two or three candidates in a handful of cells.
Two tools take the drudgery out. Auto notes, under the New Game button, fills every empty cell with its legal candidates in one tap. And when you place a digit, the board erases the matching notes from its row, column and box for you. That cleanup is on by default; the gear icon can turn it off if you want full manual control. Every control and shortcut is listed in one place on the how to play page.
Locked candidates
Look at where a digit can go inside one box. If every possible cell sits in a single row, the digit is locked to that row, and you can erase it from the rest of the row outside the box. In the position below, the 5 in the top-left box can only be in the middle row. The 5s penciled further along that row are dead, even though nobody knows yet which of the two cells holds the real 5.
The same logic runs in reverse: when a digit’s spots within a row all fall inside one box, erase it from the rest of the box. Solvers call the pair pointing and claiming, and the locked candidates guide walks both directions with boards. You only need the habit of asking where a digit is confined.
Naked pairs
When two cells in the same unit hold exactly the same two candidates, those two digits are spoken for. One cell takes each, order unknown, and every other cell in the unit loses both. Below, two cells in the row hold 2 and 7 and nothing else. The other penciled 2 and 7 in the row can be erased, which collapses those cells toward their real values.
Pairs are easiest to spot right after Auto notes, while the candidate picture is complete. Scan each row, column and box for two cells wearing identical two-digit notes. Naked pairs also scale up to triples, which is where hard puzzles pick up the thread.
Pace and habits
A medium puzzle runs 10 to 20 minutes for most players. The clock is not the point at this tier; the point is converting stalls into found techniques, and that speed comes on its own.
One habit worth building now: when you place a digit, glance at what changed. Undo is one tap away (or Ctrl+Z) and the full history survives even a closed tab, so experimenting costs nothing. When locked candidates and pairs start feeling routine, hard sudoku is waiting with the next rung of the ladder.
Frequently asked questions
What is the difference between easy and medium sudoku?
Easy puzzles fall to scanning and singles. Our medium puzzles require at least one technique beyond that: locked candidates or a naked pair. You will hit at least one point where no cell can be filled directly and you have to reason about candidates instead.
When do I need to start using pencil marks?
Medium is where notes start paying off. You only need them in the regions where the puzzle stalls, not in every cell. Tap the pencil icon and mark the two or three candidates you are unsure about.
What are locked candidates?
When a digit can only appear in one row or column within a box, it is locked there. That lets you remove the digit as a candidate from the rest of that row or column outside the box. The medium guide on this page walks through an example.
How long does a medium sudoku take?
Expect 10 to 20 minutes. The stalls are what add time, and they shrink as locked candidates and pairs become things you look for on purpose instead of stumble into.
Other difficulties
- Easy sudokuSolvable with scanning and singles. The right place to learn the habits.
- Hard sudokuHidden pairs, triples and X-wings. Full pencil marks recommended.
- Expert sudokuXY-wings, swordfish and coloring. Logic all the way, no guessing.
- Master sudokuForcing chains. The hardest puzzles we generate.