THE IDEA: NUMBERS ARE RECTANGLE SIZES
A Shikaku grid is just a square of cells with a few numbers dotted about. Every number is the area of one rectangle — and that rectangle has to contain its number. So a 4 lives inside a rectangle of exactly four cells (a 1×4 line or a 2×2 box); a 6 inside six cells (1×6, 2×3, 3×2 or 6×1), and so on.
Two rules, that's the whole game:
- Every rectangle holds exactly one number, equal to how many cells it covers.
- The rectangles tile the grid — no gaps, no overlaps. Every cell ends up inside exactly one rectangle.
That's the secret hiding in plain sight: because rectangles can't overlap or leave gaps, a lot of numbers have only ONE shape that fits. Those are your way in.
LET'S ACTUALLY SOLVE ONE — STEP BY STEP
Here's a real 7×7 Shikaku. A scattering of numbers and a lot of empty cells. Don't try to see the whole thing at once — we only ever look at one number at a time.
The starting grid — just numbers and empty cells. No rectangles drawn yet.
Step 1 — find a number with only one shape that fits.
Look at this 7 near the top. 7 is a tricky little number — you can't make 7 cells into a fat box, so it has to be a straight line of 7 cells. Could it stand up as a column? No — a column that tall would run straight through the 8 further down, and a rectangle is only allowed one number. So it can only lie flat across the top row. That's the whole grid's top edge, sorted — and we never guessed.
Step 2 — draw it in. One rectangle down.
There it is — our first rectangle, pencilled in. Notice what just happened: those top-row cells now belong to the 7. Nothing else can reach into them anymore. In Shikaku, every rectangle you draw quietly takes options away from its neighbours — and that's exactly what cracks the next one.
Step 3 — the neighbour is now forced too.
Now this 7 on the left. Same story — a 7 has to be a line of 7. A moment ago it could have stood up as a column… but the cell right above it now belongs to our first rectangle, so that door is shut. It can only lie flat across its own row. One rectangle forced the next — that's the entire feel of Shikaku.
And from here it tumbles. Each rectangle you draw eats a few cells, which kills a shape for the number next door, which forces that one… You just keep asking the same little question — "what's the only shape that still fits?" — and the grid fills itself in.
Cascading — a wide block and a few single-cell 1s fall into place off that first chain. (A 1 is always just its own cell.)
Done. Every cell sits in exactly one rectangle, and every rectangle's size matches its number. 👻
THE ONE MOVE, IN ORDER
Almost every easy Shikaku falls to the same little loop:
- Pick a number and list its shapes. A 6 can be 1×6, 2×3, 3×2 or 6×1. Each shape also has to cover the number itself.
- Throw out the impossible ones. A shape is dead if it runs off the grid, overlaps a rectangle you've already drawn, or swallows a second number.
- One survivor? Draw it. When exactly one shape is left, it's forced. And every rectangle you draw forces the next — so keep going.
Never a guess: every rectangle has a reason. Stuck? Look at the numbers near the edges and corners, or the lonely cells with only one number that can reach them.
A FEW SHORTCUTS WORTH KNOWING
You don't need these to start — but spotting them turns a slow grid into a fast one:
- 1 is free. A 1 is always just its own single cell. Fill every 1 in first — they pin down corners for the bigger rectangles.
- Prime numbers are lines. 2, 3, 5, 7… can't make a box, so they're always a straight line — which means only two possible directions to check.
- Edges and corners squeeze hardest. A number tucked against a wall has fewer directions to grow, so it's forced soonest. Start your hunt there.
And one sanity check for the end: add up every rectangle's area. It has to equal the number of cells in the grid — if it doesn't, a rectangle is the wrong size somewhere.
THAT'S IT — GO DO ONE
Find a number with only one shape that fits, draw it, and watch it force its neighbours. The first time a single forced rectangle cascades across a whole corner of the grid, you'll get why people love this one — it's a jigsaw where every piece is pure logic, no adding up, no ads mid-puzzle, just you, some rectangles, and a ghost who's quietly chuffed when the last edge clicks into place.