How hard is Shikaku 8×8?

8×8 is expert difficulty. With 64 cells and numbers up to 64, you'll need strong factor decomposition skills and the ability to plan 3-4 steps ahead. Typical solve time is 15-25 minutes.

Is 8×8 the standard Shikaku size?

8×8 is one of the most common sizes in Nikoli's published Shikaku puzzles. It's considered the 'standard' expert grid — large enough for complex logic, small enough to fit on a magazine page.

What's the difference between 8×8 and 10×10 Shikaku?

8×8 has 64 cells with numbers up to 64; 10×10 has 100 cells with numbers up to 100. The 10×10 introduces numbers with many more factor pairs (like 60 = 2×30, 3×20, 4×15, 5×12, 6×10) and takes roughly twice as long to solve.

Shikaku 8×8 — The Classic Expert Grid

The 8×8 grid is Shikaku's "standard" expert size — the one Nikoli publishes most often. With 64 cells and numbers up to 64, it demands sharp factor decomposition and multi-step planning.

▶ Play 8×8 Shikaku Now

Why 8×8 is the Benchmark

64 cells — a perfect square (8²), creating natural symmetry
12-18 rectangles — complex enough for deep logic chains
15-25 minute solve time — a proper puzzle session
Even-width grid — no true center cell, symmetric constraints on both halves

8×8-Specific Strategies

The "64 Check"

All numbers must sum to 64. With 12-18 numbers, quick mental addition is essential. Group numbers into pairs that sum to 10 for faster checking.

Even-Width Advantage

Unlike 7×7, the 8×8 grid has perfect bilateral symmetry. If you solve the left half, the right half often follows similar patterns. Use this to cross-check your placements.

The "Big Number" Rule

Numbers above 32 in an 8×8 grid are extremely constrained. A "48" must be 6×8 (covering most of the grid). A "56" must be 7×8. These large numbers effectively partition the grid into regions before you place anything else.

Key Factor Pairs for 8×8

Number	Factor Pairs (fit in 8×8)	Notes
12	2×6, 3×4, 4×3, 6×2	Most flexible mid-range number
16	2×8, 4×4, 8×2	4×4 square is a strong anchor
24	3×8, 4×6, 6×4, 8×3	Four options — check surroundings
32	4×8, 8×4	Half the grid — very constrained
48	6×8, 8×6	Covers 75% of grid
56	7×8, 8×7	Covers 87.5% of grid

Advanced Technique: Region Counting

1Identify "islands". Numbers surrounded by other numbers form isolated regions. Count the cells in each region — they must be covered by the numbers inside them.

2Sum-check regions. If a region has 12 cells and contains numbers 4, 3, 5 — they sum to 12. Perfect fit. If they sum to 11, something's wrong.

3Eliminate impossible shapes. For each number in a region, list all possible rectangles. If only one fits the region constraints, lock it in.