Mini Sudoku (4×4 and 6×6): Rules & How to Solve

Both VariantDoku dailies are small boards. The variant rules stay the same — only the digits run out sooner, and that changes almost every number you rely on.

The rule
On 4×4 and 6×6 boards
Frequently asked questions

The rule

Fill a 4×4 board with 1–4, or a 6×6 board with 1–6, so that every row, column and box holds each digit once. Boxes are 2×2 on 4×4 and two rows by three columns on 6×6. Variant clues work exactly as on 9×9.

The two small boards at a glance.
Board	Digits	Box	Row, column and box total
4×4	1–4	2×2	10
6×6	1–6	2 rows × 3 columns	21

How to solve 4×4 and 6×6 sudoku

Use the 10 and 21 rules

A house adds up to 10 on a 4×4 board and 21 on a 6×6 board. Subtract cage totals, arrow sums or known digits from it exactly as you would from 45 on a 9×9 board.

Work the two boxes of a 6×6 row

Each 6×6 row passes through just two boxes, each covering two rows. Once you know which row of one box holds a digit, the same digit in the box beside it must sit in that box's other row.

One pair solves half a 4×4 house

A 4×4 house has four cells, so a pair of cells that can only be {a,b} leaves the other two cells with exactly the two remaining digits — every pair you find is half the house.

Re-read the variant numbers

Most variant facts get stronger on small boards: a black Kropki dot on 4×4 always contains a 2, an X on 6×6 is always {4,6}, and a 6×6 whispers line holds only 1s and 6s. The cheat sheet below lists them all.

Worked examples on small boards

6×6: 11 = {5,6} and 6 = {1,2,3}, so the box's last cell is 21 − 11 − 6 = 4.

Killer Sudoku →

6×6: on a five-cell thermometer every cell has exactly two candidates.

Thermometer Sudoku →

6×6: three different shaft digits force a circle of 6 and the set {1,2,3}.

Arrow Sudoku →

4×4: a black dot always holds a 2, so 2 leaves the rest of its row and box.

Kropki Sudoku →

6×6: an X is always {4,6}, so 4 and 6 leave the rest of its row and box.

XV Sudoku →

6×6: a four-cell renban always holds 3 and 4, so they leave the rest of its box.

Renban Sudoku →

6×6: a whispers line is made only of alternating 1s and 6s.

German Whispers Sudoku →

4×4: two different middle cells force circles of 1 and 4 and middles of 2 and 3.

Between Line Sudoku →

Cheat sheet: every variant on small boards

Killer Sudoku

Cage sums that allow only one set of digits.
Board	Cage	Sums with only one combination
4×4	2 cells	3: {1,2} · 4: {1,3} · 6: {2,4} · 7: {3,4}
4×4	3 cells	6: {1,2,3} · 7: {1,2,4} · 8: {1,3,4} · 9: {2,3,4}
6×6	2 cells	3: {1,2} · 4: {1,3} · 10: {4,6} · 11: {5,6}
6×6	3 cells	6: {1,2,3} · 7: {1,2,4} · 14: {3,5,6} · 15: {4,5,6}
6×6	4 cells	10: {1,2,3,4} · 11: {1,2,3,5} · 17: {2,4,5,6} · 18: {3,4,5,6}
6×6	5 cells	15: {1,2,3,4,5} · 16: {1,2,3,4,6} · 17: {1,2,3,5,6} · 18: {1,2,4,5,6} · 19: {1,3,4,5,6} · 20: {2,3,4,5,6}

Thermometer Sudoku

Candidates for each cell of a thermometer, from bulb to tip.
Board	Length	Candidates, bulb to tip
4×4	2 cells	1–3 · 2–4
4×4	3 cells	1–2 · 2–3 · 3–4
4×4	4 cells	1 · 2 · 3 · 4
6×6	2 cells	1–5 · 2–6
6×6	3 cells	1–4 · 2–5 · 3–6
6×6	4 cells	1–3 · 2–4 · 3–5 · 4–6
6×6	5 cells	1–2 · 2–3 · 3–4 · 4–5 · 5–6
6×6	6 cells	1 · 2 · 3 · 4 · 5 · 6

Arrow Sudoku

Arrows whose shaft cells all see each other.
Board	Shaft (cells all different)	Smallest sum	Circle
4×4	2 cells	3	3–4
4×4	3 cells	6	impossible
4×4	4 cells	10	impossible
6×6	2 cells	3	3–6
6×6	3 cells	6	6 = 1+2+3
6×6	4 cells	10	impossible

Kropki Sudoku

Every digit pair a Kropki dot can mark.
Board	Black-dot pairs	Never on a black dot	White-dot pairs
4×4	{1,2} {2,4}	3	{1,2} {2,3} {3,4}
6×6	{1,2} {2,4} {3,6}	5	{1,2} {2,3} {3,4} {4,5} {5,6}

Renban Sudoku

Every run a renban line can hold, and the digits it always contains.
Board	Length	Possible runs	Always on the line
4×4	2 cells	1–2 · 2–3 · 3–4	none
4×4	3 cells	1–3 · 2–4	2, 3
4×4	4 cells	1–4	1, 2, 3, 4
6×6	2 cells	1–2 · 2–3 · 3–4 · 4–5 · 5–6	none
6×6	3 cells	1–3 · 2–4 · 3–5 · 4–6	none
6×6	4 cells	1–4 · 2–5 · 3–6	3, 4
6×6	5 cells	1–5 · 2–6	2, 3, 4, 5
6×6	6 cells	1–6	1, 2, 3, 4, 5, 6

German Whispers Sudoku

Digits that may sit side by side on a German whispers line.
Board	Legal neighbours
4×4	none — no two digits are 5 apart
6×6	1 → 6 · 6 → 1

XV Sudoku

Every digit pair an X or a V can mark.
Board	V (5)	X (10)
4×4	{1,4} {2,3}	none
6×6	{1,4} {2,3}	{4,6}

Frequently asked questions

What is mini sudoku?

Mini sudoku usually means a 6×6 grid with digits 1–6 and boxes two rows tall and three columns wide; a 4×4 grid with 2×2 boxes is smaller still. The rules are the same as classic sudoku with fewer digits.

How do you solve a 6×6 sudoku?

Place 1–6 once in every row, column and 2×3 box. Scan for hidden singles, use the fact that each row crosses only two boxes, and lean on the variant clues — they become far more restrictive with only six digits.

What does a row add up to in 4×4 and 6×6 sudoku?

10 on a 4×4 board (1+2+3+4) and 21 on a 6×6 board (1+2+3+4+5+6). Use these totals like the 45 rule.

Are VariantDoku's daily puzzles 4×4 and 6×6?

Yes. Every day brings a new 4×4 and a new 6×6 daily with a leaderboard of clean-solve times, alongside a catalog of 4×4, 6×6 and 9×9 puzzles.

Can German whispers appear on a 4×4 board?

No. The rule needs neighbours at least 5 apart, and no two digits from 1–4 are. On 6×6 boards a whispers line uses only 1 and 6.

Play Mini Sudoku (4×4 and 6×6) in VariantDoku

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