Play Fillomino Online
Fill every cell with a number so that each connected group of identical digits forms a polyomino whose size equals the number.
Tap a cell, then pick a number
What Is Fillomino?
Fillomino, also known as Polyominous, is a number-placement logic puzzle first published by the Japanese puzzle company Nikoli. The name derives from the idea of “filling” a grid with polyominoes — connected groups of cells with the same number.
The puzzle is played on a rectangular grid. Some cells are pre-filled with numbers (called givens or clues). Your task is to fill every empty cell with a positive integer so that each connected group of identical numbers (an orthogonally connected region) contains exactly as many cells as the number itself. For example, all cells in a group labelled “4” must form a connected polyomino of exactly four cells.
Unlike Sudoku, Fillomino has no row or column uniqueness constraints. Instead, the puzzle revolves entirely around polyomino sizes, region connectivity, and the rule that no two groups sharing the same number may be orthogonally adjacent. This key constraint — sometimes called the no-merge rule — gives Fillomino its distinctive deductive character.
Rules of Fillomino
- Fill every cell: Every cell in the grid must contain a positive integer.
- Group size equals number: Each connected group of identical numbers (orthogonally adjacent cells sharing the same digit) must contain exactly as many cells as the value of that digit. A group of 3s has exactly three cells; a group of 5s has exactly five cells.
- No same-number adjacency between groups: Two distinct groups with the same number cannot be orthogonally adjacent. If they were, they would merge into a single larger group, violating the size constraint.
- Numbers are not limited to givens: You may write any positive integer in a cell, including numbers that don’t appear as clues. Some solutions require the solver to introduce new numbers.
- Unique solution: A well-formed Fillomino puzzle has exactly one solution, reachable through pure logic with no guessing.
How to Solve Fillomino Puzzles
1. Merge Adjacent Identical Clues
When two (or more) cells with the same number are orthogonally adjacent, they must belong to the same group. This immediately tells you part of the group’s shape. For instance, two adjacent 4s means those two cells are already part of a four-cell group — you need to find exactly two more connected cells for that group.
2. Separate Different-Numbered Neighbours
If a cell labelled 3 is next to a cell labelled 5, they belong to different groups. The boundary between them is fixed. This is less of an action step and more of a mental note — but it constrains how each group can expand.
3. Complete Small Groups First
A clue of 1 is immediately complete — that single cell is its own group. All orthogonal neighbours must contain a different number (and none of them can be 1). Similarly, two adjacent 2s are a complete domino — mark their borders and move on. Completing small groups early reduces uncertainty elsewhere.
4. Look for Forced Expansions
If a group still needs to grow but can only expand in one direction (because other directions are blocked by completed groups or grid edges), those cells are forced. For example, a lone 3-clue in a corner can only extend along the two adjacent edges.
5. Use the No-Merge Rule
The constraint that two groups with the same number cannot touch is powerful. If placing a certain number in a cell would cause two separate groups of that number to become adjacent (and hence merge into a group that is too large), that placement is impossible. This rule is the backbone of advanced Fillomino deduction.
6. Introduce New Numbers When Needed
Not every number in the solution appears as a given. If an empty region is surrounded by completed groups and has, say, six cells, those six cells must all contain 6 — even if 6 never appeared as a clue. Recognising when to introduce new numbers is a hallmark of experienced Fillomino solving.
Grid Sizes & Difficulty Levels
- 7×7 — Easy: Compact grid with many given numbers. Ideal for learning the rules and practising basic techniques like merging and separating clues.
- 7×7 — Medium/Hard: Same grid size but fewer clues and larger polyominoes, requiring longer deduction chains and no-merge reasoning.
- 10×10: The classic Fillomino experience. A balanced mix of small and large polyominoes with room for interesting interactions.
- 14×14: Large grids for experienced solvers. Expect longer solve times, more introduced numbers, and deeper logical chains.
Fillomino vs Other Logic Puzzles
- vs Sudoku: Both fill a grid with numbers, but Sudoku uses row/column/box uniqueness while Fillomino uses connected-group size constraints. Fillomino allows repeated numbers in rows and columns.
- vs Nurikabe: Both partition a grid into regions anchored by number clues. Nurikabe classifies cells as sea or island; Fillomino fills every cell with a number. Nurikabe has a single connected sea; Fillomino has no such global connectivity rule.
- vs Suguru (Tectonic): Both involve filling irregular regions with numbers. In Suguru the regions are given; in Fillomino, determining the regions is the puzzle.
- vs Shikaku: Both tile a grid with polyominoes anchored by number clues. Shikaku restricts shapes to rectangles; Fillomino allows any polyomino shape.
Frequently Asked Questions
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