5 × 5 Shikaku puzzles — 25 cells, a handful of rectangles, solved in a minute or three. The right size to learn the rules or squeeze in a quick round.

7 × 7 Shikaku puzzles — the coffee-break size. Enough room for real deduction chains, still solvable in a few minutes.

10 × 10 Shikaku puzzles — the classic size. 100 cells, 15–30 rectangles, and every solving technique in play. A proper session without an all-day commitment.

15 × 15 Shikaku puzzles — 225 cells for solvers who want a long, layered solve. Deep deduction chains and regions that unlock in stages.

20 × 20 Shikaku puzzles — the giant size. 400 cells, 40+ rectangles, and an hour of sustained deduction. Every board verified to a single solution.