The rules in 20 seconds
Cut the grid into rectangles. Each rectangle holds one number, and that number is how many cells it covers. That’s it. (Squares count as rectangles.) The full version with diagrams is on how to play.
Let’s solve one together
Here is an easy 5×5 Shikaku. Its numbers add up to 25 — the number of cells — which is always true. Step through the solution, reading each reason:
- Step 1Prime numberThe 5 at row 5, column 1 has only one possible rectangle from the start — 5 is prime, so it must be a straight strip, and every other position would cross the edge of the grid or swallow another number. Draw the 1×5 rectangle.
- Step 2Prime numberThe 3 at row 5, column 3 has only one possible rectangle from the start — 3 is prime, so it must be a straight strip, and every other position would cross the edge of the grid or swallow another number. Draw the 1×3 rectangle.
- Step 3Prime numberThe 3 at row 5, column 4 has only one possible rectangle from the start — 3 is prime, so it must be a straight strip, and every other position would cross the edge of the grid or swallow another number. Draw the 1×3 rectangle.
- Step 4Prime numberThe 2 at row 5, column 2 has only one possible rectangle from the start — 2 is prime, so it must be a straight strip, and every other position would cross the edge of the grid or swallow another number. Draw the 1×2 rectangle.
- Step 5Only optionThe 3 at row 2, column 2 started with 3 possible rectangles, but the rectangles and claimed cells around it now rule out all but one. It must be 1×3.
- Step 6Prime numberThe 2 at row 5, column 5 has only one possible rectangle from the start — 2 is prime, so it must be a straight strip, and every other position would cross the edge of the grid or swallow another number. Draw the 1×2 rectangle.
- Step 7Only optionThe 3 at row 3, column 5 started with 3 possible rectangles, but the rectangles and claimed cells around it now rule out all but one. It must be 1×3.
- Step 8Only optionThe 4 at row 2, column 4 started with 4 possible rectangles, but the rectangles and claimed cells around it now rule out all but one. It must be 2×2.
Three beginner habits
- Start where options are few: corners, edges, prime numbers and big numbers in tight spaces.
- Only draw what is certain. If you are choosing between two shapes, look elsewhere first.
- Re-check neighbours after every rectangle. Each rectangle is a new wall.
Common beginner mistakes
- Forgetting that a 4 can be a 2×2 square, or a 9 a 3×3.
- Drawing a rectangle that covers the right area but leaves a cell nobody else can reach.
- Guessing. Every puzzle on this site can be solved by reasoning alone.
Where next
Play a few 5×5 puzzles, then read the strategy guide and watch a full 7×7 solve.
Play this puzzle yourself
The same 5×5 grid on the interactive board.
Questions
Is Shikaku good for beginners?
Yes. The rules fit in one sentence and small 5×5 grids take a minute or two, yet the same ideas scale up to very hard puzzles.
What size should a beginner start with?
Start with 5×5 Easy, move to 7×7 once it feels natural, then try 10×10 — the classic newspaper size.
Do I need to be good at maths?
Only small multiplication — knowing that 6 = 2 × 3 or 12 = 3 × 4. The real skill is logical reasoning.