What Is Shikaku?

Published Apr 16, 2026 3 min read

Shikaku is a rectangle partition puzzle. You start with a grid that contains a few numbered cells. Your job is to divide the entire board into rectangles so that each rectangle contains exactly one number, and the area of that rectangle matches the number inside it.

That simple rule set is what makes the puzzle so clean. You do not need arithmetic tricks or hidden wordplay. You only need to reason about shape, area, and how one valid rectangle changes the options around it.

Basics Beginner Friendly Rules

Main idea

One reason Shikaku feels satisfying is that progress compounds. A small clue with only one or two possible shapes can lock down part of the board. Once those cells are claimed, larger clues...

Overview

One reason Shikaku feels satisfying is that progress compounds. A small clue with only one or two possible shapes can lock down part of the board. Once those cells are claimed, larger clues become easier to place. The puzzle often feels open at the start and surprisingly constrained a few moves later.

If you are brand new, the best path is simple: learn the rules, play a few small boards, and then check your thinking with the solver when you get stuck.