Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
What is Medium Sudoku?
Medium Sudoku is classic sudoku with fewer digits to start from: every board on this page has 32 of the 81 squares filled and exactly one answer. Each row, column and 3×3 box must end up holding the digits 1 to 9 once. It is the level the main sudoku page opens on, and the one most people settle into for a daily game.
Like Easy, Medium never needs anything beyond the two simplest steps in the game. What changes is which of the two does the work — and that is enough to make it feel like a different puzzle.
What changes from Easy?
We dealt 200 Medium boards from this page’s own generator and tried each with one step at a time. Naked singles alone finished only 80 of them, against 192 of 200 on Easy. Hidden singles alone finished 191, and the two together all 200. So on Medium you cannot wait for a square to show a single digit: most of the time you have to go looking for where a digit fits.
| Level | Given digits | Singles alone finish | What the rest need |
|---|---|---|---|
| Easy | 40 | 200 of 200 | Nothing more |
| Medium | 32 | 200 of 200 | Nothing more |
| Hard | 26 | 171 of 200 | Locked candidates finish all 29 |
| Expert | 22–25 (median 23) | 135 of 200 | Locked candidates finish 47 more; naked pairs the last 18 |
200 boards a level, dealt by this page’s own generator and measured on 10 October 2026; every one had exactly one answer, counted by a separate solver. “Singles” means naked and hidden singles together. Nothing past naked pairs was needed on any board.
Nothing past singles is needed on any Medium board. Pointing pairs and box/line reduction start at Hard; if a Medium board seems to call for them, a single has been missed.
How do you find a hidden single when no square is obvious?
The board above has no naked single anywhere at the start, so the way in has to be a hidden single. Choose a digit and a box that lacks it, then follow that digit’s copies along their rows and columns until only one square of the box is left uncovered. Doing it for every box with one digit before moving to the next is the fastest way to work a Medium board, because each digit you place covers more squares for the next box along. The hidden singles guide goes further, rows and columns included.
Start with the digit placed most often: it has the fewest boxes left to fill and the most copies covering them. When it is done, take the next most common. The rare digits come last, when the board around them is fuller.
When are notes worth it on Medium?
Most Medium boards can be finished without writing anything down, but notes pay off when a whole round of scanning turns up nothing. Pencil marks show the hidden singles too: a digit written in only one square of a row, column or box goes there. Start Notes fills in every candidate at once, and when you place a correct digit the game clears it from the notes of every square it sees, so the marks stay honest as you go.
Has this page always dealt boards like these?
No. From 28 March 2026, when the page went up, until 13 April, its generator blanked squares at random until 32 were left and checked nothing. Run again, 194 of 200 of its Medium boards had more than one answer — and the game marks digits against one stored answer, so a digit that broke no rule could be marked wrong.
From 13 April every board had one answer, but the generator did not look at how a board could be solved. Measured then, 3 of 40 Medium boards needed more than singles, locked candidates, pairs and the fish patterns our solver tries, while this page promised that every one “can still be solved purely through logical deduction, no guessing required”. It also listed box/line reduction as a Medium technique. Since 10 October 2026 singles finish every Medium board, and the numbers here are measured from the generator as it is now.
What do the buttons do?
- Notes switches the keypad to pencil marks, and Start Notes fills every empty square with the digits it can still hold, in one go.
- Hint picks a square at random from the ones that are empty or wrong and puts its answer in. It does not explain the step and it is an ordinary move: Undo takes it back.
- Undo and Redo step back and forward through your moves (Ctrl+Z and Ctrl+Y, or Cmd on a Mac); Erase clears the selected square.
- A wrong digit turns red and adds one to the mistake count. There is no limit: the count never ends the game.
- Solve asks before it fills the grid. New Game deals another Medium board, and the level buttons above the grid switch level without leaving the page.
- The timer starts when the board is dealt and runs until it is finished. This page keeps its own saved board, apart from the main sudoku page’s, so you can have one game going on each.
Where next?
When Medium boards stop slowing you down, Hard adds the first step beyond singles, on boards that start with six fewer digits. Easy is there for a quicker game. Daily Medium Sudoku deals one new Medium board a day, the same for everyone, and on the main daily sudoku Wednesday and Thursday are Medium too. For paper, the printable sudoku page has PDFs at every level.