Classic Cube: sudoku in 3D
The Classic Cube: six sudokus linked by their edges
The Classic Cube puts a 9×9 sudoku grid on each of the six faces of a 3D cube. Turn it with your mouse or your finger, then select a face: it lies flat, full size, and plays like a regular sudoku. The difference from six ordinary grids lies at the edges: just like on a Rubik's Cube, an edge cell belongs to two faces, and a corner cell to three.
Here, a face can never be solved on its own: it is missing digits, and you fill in its edges by making progress on its neighbours. So you work your way around the cube, from one face to the next, in any order you like. A face filled in without errors turns gold; six gold faces, and the cube is won.
No new rule to learn: if you can play 9×9 sudoku, you can play the cube. Sudoku-Land offers it in 3 levels (easy, medium, hard), with 100 different cubes per level: the game first gives you a cube you have never started. You get notes mode, six hints for the whole cube, autosave, a dark theme and the ⚙️ Settings menu. Every cube has a single solution and can be solved by logic alone, without ever guessing. It is the first of the site's three sudoku cubes, free and with no sign-up, on desktop and mobile alike.
Classic Cube rules
- Each face is a sudoku — every row, every column and every 3×3 box of a face contains the numbers 1 to 9, once each.
- The edges are shared — a cell on the border of a face is also on the border of the neighbouring face: the digit you place there shows on both faces and must be correct for both. A corner cell belongs to three faces.
- One face alone is not enough — it does not have enough starting numbers to be solved: its neighbours bring it more through the edges.
- Six gold faces, cube won — a face filled in without errors turns gold and locks, along with the cells it shares with its neighbours.
Tips for solving the Classic Cube
- When a face gets stuck, move to its neighbour — the digits found on the shared edge often unlock the first face. The arrows on the edges of the flat face, or Shift + arrow on the keyboard, bring up the face next to it.
- Look at the edges first — an edge cell follows the rules of two faces at once: that is often where a digit turns up fastest.
- Keep an eye on the face buttons — the golden ring of each button, from 1 to 6, shows how far along its face is. The Esc key, or the cube-shaped button, turns the cube back to a three-quarter view.
- Pencil in candidates — with notes mode (Space, right-click or long press), or with the auto notes of the face in play, which you can turn on in the ⚙️ Settings menu: they take into account the cells shared with the neighbouring faces.
Other cubes and puzzles
Frequently asked questions
What is the Classic Cube?
It is a three-dimensional sudoku: six 9×9 grids, one on each face of a cube that you turn with your mouse or your finger. Each face follows the usual sudoku rules, and neighbouring faces share the cells along their borders. The cube is won when all six faces are filled in.
What does “shared edges” mean?
Think of the cube as a Rubik's Cube where each small cube carries a single digit. A cell on the border of a face is also on the border of the neighbouring face: the digit you place there shows on both faces, and it must be correct for both. A corner cell even belongs to three faces. That is why the cube has 386 cells, not 6 × 81 = 486.
Why can't a face be solved on its own?
Because it starts with too few numbers: its neighbours supply more, through the cells of their shared edges. So you have to work your way around the cube, moving from one face to another in any order you like. Every cube still has a single solution, which you can find by logic, without guessing.
How many hints do you get per cube?
Six for the whole cube, to use on the face of your choice. A hint reveals the digit of the selected cell. Auto notes, which you can turn on in the Settings menu, also cost a hint when you choose “Cleaned candidates”; “All candidates” stays free.
Can you play the Classic Cube on a phone?
Yes. Tap a face: it lies flat and takes up almost the full width of the screen. A long press on a cell switches to notes mode, and the buttons 1 to 6 below the cube let you change faces without turning it. Your cube is saved automatically on your device.