How to play the tetromino puzzle
- Look at the board. Each level is a wooden board, sometimes with dark pegs that cannot be covered. The pieces in the tray cover exactly the free squares.
- Drag a piece onto the board. Touch or click a piece and drag it over the board. A green outline shows where it will snap; red means it overlaps something.
- Turn and flip. Tap a selected piece (or press Turn) to rotate it 90°, and press Flip for its mirror image. On a keyboard, R turns and F flips.
- Move or take back pieces. Drag a placed piece to a new spot, or drag it off the board to return it to the tray. Undo steps back one move.
- Fill every square. The level is solved when every free square is covered. Stuck? Hint places one correct piece for you.
The five tetrominoes
Turning and flipping allowed, these five are all the ways to join four squares. Counted as one-sided pieces (mirror images different) there are 7, and counting every turn and flip separately there are 19 — the numbers our level generator works with.
Tetromino puzzle strategy
- Fill corners and edges first. Corners only accept a few shapes, so they decide the rest of the board.
- Watch for tiny gaps. A pocket of 1, 2 or 3 squares can never be filled, so undo before you place a piece that leaves one.
- Count squares in fours: any closed-off region must have a multiple of 4 squares or it is already a dead end.
- Save the T for last. It is the only piece that covers three squares of one chessboard colour, so it fixes balance problems at the end.
- Straight pieces love long edges; the square needs a 2×2 space, which gets rare late in a level.
Why some boxes are impossible
The five different tetrominoes cover 20 squares, so it is natural to try a 4×5 rectangle. Our exact-cover solver checks every arrangement and finds 0 solutions for 4×5 and 0 for 2×10. The reason is the chessboard colouring: each piece covers two dark and two light squares, except the T, which covers three of one colour and one of the other. Use two of each piece instead and a 4×10 rectangle is easy:
All levels at a glance
Every level was generated from a random wooden board, then checked with the same Dancing Links search that powers our pentomino solver. Fewer solutions usually means a harder level.
| Level | Board | Pegs | Pieces | Solutions |
|---|---|---|---|---|
| 1 | 4 × 2 | 0 | O O | 1 |
| 2 | 4 × 3 | 0 | I L L | 2 |
| 3 | 4 × 4 | 0 | I I L L | 6 |
| 4 | 4 × 4 | 0 | I I O O | 6 |
| 5 | 5 × 4 | 0 | I O S L L | 16 |
| 6 | 6 × 3 | 2 | T S L L | 5 |
| 7 | 5 × 4 | 0 | I I T T S | 2 |
| 8 | 5 × 5 | 1 | I O O O T T | 2 |
| 9 | 6 × 4 | 0 | I I T T S S | 4 |
| 10 | 6 × 4 | 0 | O T T S L L | 8 |
| 11 | 5 × 5 | 1 | I I I I T L | 1 |
| 12 | 6 × 5 | 2 | I O O T L L L | 7 |
| 13 | 7 × 4 | 0 | O O T T S S L | 24 |
| 14 | 6 × 5 | 2 | I I T T S S L | 2 |
| 15 | 6 × 6 | 4 | I I O O O T S L | 4 |
| 16 | 8 × 4 | 0 | I I O T T S S L | 100 |
| 17 | 7 × 5 | 3 | I O T T T S S L | 8 |
| 18 | 6 × 6 | 0 | I I O O T T S S L | 336 |
| 19 | 6 × 6 | 4 | I O T T S S S L | 3 |
| 20 | 7 × 6 | 2 | I I I I I I O T S L | 34 |
| 21 | 8 × 5 | 0 | I I I I I O T T S L | 484 |
| 22 | 6 × 7 | 2 | I I I O T T S S S L | 171 |
| 23 | 7 × 6 | 2 | I I I O T T T T S L | 63 |
| 24 | 8 × 5 | 0 | I I I O O T T S L L | 2,568 |
More shape puzzles
Ready for bigger pieces? The hexomino puzzle uses six squares per piece. For five, learn the 12 pentomino shapes, try the 8×8 pentomino puzzle, or play the free 8×8 packing puzzle with 100 levels. Teaching children? See pentominoes for kids and the printable pieces.