How to Play Shikaku
New to Shikaku — also sold as Divide by Box or Rectangles? The whole game is one idea: cut the grid into rectangles so each rectangle holds exactly one number, and that number equals the rectangle’s area. No arithmetic beyond width × height, no guessing — every board has a single answer you can reason out. This guide takes you from zero to your first solved grid.
How to play Shikaku, step by step
- Read the grid — it starts scattered with numbers; every number will end up inside its own rectangle, and every cell will belong to exactly one rectangle.
- Understand a number — it names an area: a 4 means a rectangle covering 4 cells (1×4, 4×1 or 2×2) that contains that 4 and no other number.
- Start with the 1s — a 1 is always a single cell; mark it and it is done.
- Do the corner and edge numbers next — a number near a corner has few ways to extend, so its rectangle is often forced from the start.
- Use prime numbers — 2, 3, 5 and 7 can only be straight strips, which makes their placement easy to prove.
- Never cover a second number — a rectangle that would swallow another clue is illegal; this rules out most wrong shapes for you.
- Fill every cell — when you finish, the rectangles tile the whole grid with no gaps and no overlaps. If a cell is left orphaned, revisit the nearest large number.
The three rules, in plain words
Rectangles only · one number per rectangle · area = number. That is the entire rulebook. Everything else — corners, primes, factor pairs — is just strategy for finding which rectangle each number must own. If you can multiply width by height, you can play Shikaku.
When you are comfortable with the rules, the tips & strategy guide shows the techniques that crack bigger boards, and the free online Shikaku lets you practise on 5×5 and 7×7 grids with a shared daily puzzle.
Your first board, walked through
Solve your first board in this order: 1s → corner numbers → primes → everything else. The 1s cost nothing. A corner 2 has only two possible positions, and any neighbouring number usually eliminates one — draw it in. A 3 or 5 is a straight strip; check which direction fits without swallowing another clue. Each rectangle you commit removes cells from every remaining number’s options, so the board gets easier as you go — the opposite of guessing, where one wrong shape quietly breaks a corner you will not notice until the end.
How to play Shikaku: FAQ
What do the numbers in Shikaku mean?
Each number is the area of the rectangle that must contain it — a 6 sits inside a rectangle covering exactly 6 cells (1×6, 6×1, 2×3 or 3×2), with no other number inside.
Can rectangles overlap or leave gaps?
No. The finished board is a perfect tiling: every cell belongs to exactly one rectangle, with no overlaps and no empty cells left over.
Do I ever need to guess?
No — every board here has one solution reachable by logic alone. If you feel stuck, look for a corner number, a prime, or a cell that only one number’s rectangles can reach.
Is Shikaku the same as Divide by Box?
Yes — Shikaku is the original Japanese name, and the same puzzle is published in English as Divide by Box or Rectangles.