Small Cubes: 3D sudoku for beginners
Small cubes: 3D sudoku, one step at a time
The small cubes are the gateway to 3D sudoku. As in the Classic Cube, each face of a cube carries a sudoku grid, and neighbouring faces share the cells along their borders. But here the grids are smaller: 2×2, 4×4, 6×6, then 8×8. You learn to work your way around the cube on the 2×2, with 8 digits to find, before taking on the 8×8 and its 296 cells.
Turn the cube with your mouse or your finger, then select a face: it lies flat and plays like a regular grid. The digits are in colour, as in the site's Kids, Junior and Junior+ grids. A face filled in without errors turns gold, and its face button fills with gold as you go: six gold faces, and the cube is won.
Start with the 2×2: each cell is a corner of the cube, shared by three faces. So there are only eight digits to find, and each face contains 1, 2, 3 and 4. Each size has three levels (easy, medium, hard), and all of them can be solved with the two basic sudoku reflexes, without ever guessing. The hard 8×8 is close to the Classic Cube's medium level: from there, the 9×9 is just one step away. Each size keeps its cube in progress, the game first gives you a cube you have never started, and everything is free, with no sign-up, on desktop and mobile alike.
Small cube rules
- Each face is a small sudoku — in 4×4, every row, every column and every 2 × 2 box contains 1, 2, 3 and 4; in 6×6, the numbers 1 to 6, with boxes of 2 rows by 3 columns; in 8×8, the numbers 1 to 8, with boxes of 2 rows by 4 columns.
- The 2×2 — each face has only 4 cells: it contains 1, 2, 3 and 4, once each.
- The edges are shared — a cell on the border of a face also belongs to the neighbouring face, and a corner cell to three faces: the digit you place there counts for each of them. On the 2×2, every cell is a corner.
- 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 to get started
- The key to the 2×2 — two opposite corners of the cube, at both ends of a diagonal running through it, always carry the same digit. So a given digit already tells you where its twin goes.
- 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.
- Watch the face buttons — each square button fills with gold as its face fills in: you can see at a glance how far along you are. The Esc key, or the cube-shaped button, turns the cube back to a three-quarter view.
- Move up a size when you are ready — after each win, the “Congratulations” card offers you the next cube; after the 8×8, the Classic Cube is waiting for you.
Other cubes and puzzles
Frequently asked questions
What are the small cubes?
They are three-dimensional sudokus, only smaller: a cube you turn, with a 2×2, 4×4, 6×6 or 8×8 grid on each face. Neighbouring faces share the cells along their borders, as in the Classic Cube. It is the gentlest way to discover 3D sudoku.
Which cube should I start with?
The easy 2×2: eight digits to find (one per corner of the cube), from 1 to 4, and a few minutes to see how the faces share their borders. The cubes then unlock one after the other, from the easy 2×2 to the hard 8×8: each cube you solve unlocks the next one, and the “Congratulations” card takes you there. Already know 3D sudoku? Tap a size that is still locked, then “Unlock everything”.
Why is there no 3×3, 5×5 or 7×7 cube?
Because a sudoku face needs boxes that hold as many cells as a row: 4 cells fit into 2 × 2 boxes, 6 into 2 × 3 boxes, 8 into 2 × 4 boxes. With 3, 5 or 7 cells per row, no such split is possible, and the rule would change from one cube to the next.
Do you need to know complicated techniques?
No. All the small cubes can be solved with two reflexes: look for the only cell where a digit can go in a row, a column or a box, and for the only digit that can go in a cell. The difficulty comes from the number of starting digits and from the cells you have to find by turning the cube. Every cube has a single solution, which you can find without ever guessing.
Can you play the small cubes 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 face buttons let you change faces without turning the cube. Each size keeps its cube in progress, saved automatically on your device.