You do not need to guess to solve the 4×4 example in this guide: each row, column, and box must contain the numbers 1 to 4 once. If a harder puzzle leaves you without an obvious deduction, that does not mean every sudoku can be solved with the same beginner techniques. This smaller grid lets you focus on one deduction at a time.
Start with a 4×4 grid
A 4×4 sudoku uses the numbers 1 through 4. Each row, column, and 2×2 box must contain each number once. There is no adding; the rule is simply that a number cannot repeat.
This example is almost solved so you can focus on one cell. Which number belongs in place of the question mark?
| Column 1 | Column 2 | Column 3 | Column 4 | |
|---|---|---|---|---|
| Row 1 | 1 | 2 | 3 | ? · blank |
| Row 2 | 3 | 4 | 1 | 2 |
| Row 3 | 2 | 1 | 4 | 3 |
| Row 4 | 4 | 3 | 2 | 1 |
Show the deduction
The first row already contains 1, 2, and 3, so it is missing 4. The last column contains 2, 3, and 1, so it is missing 4 as well. The top-right box contains 3, 1, and 2, so the 4 fits. We did not try a number at random; we found the only number that can go there.
An intermediate step: two deductions in a 6×6
Use numbers 1 through 6 and boxes two rows high by three columns wide. A is R1C2 and B is R1C1. Three numbers are missing from the first row; check the columns to decide where to start.
| Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 | |
|---|---|---|---|---|---|---|
| Row 1 | B · blank | A · blank | 3 | 4 | Blank | 6 |
| Row 2 | 4 | 5 | 6 | 1 | 2 | 3 |
| Row 3 | Blank | 3 | 4 | Blank | 6 | 1 |
| Row 4 | 5 | 6 | 1 | Blank | Blank | 4 |
| Row 5 | 3 | 4 | 5 | 6 | 1 | Blank |
| Row 6 | 6 | 1 | Blank | Blank | 4 | Blank |
First deduction: what goes in A?
Row 1 is missing 1, 2 and 5. Column 2 already contains 5, 3, 6, 4 and 1: rule out 1 and 5. Only 2 remains. The top-left box contains 3, 4, 5 and 6, so it does not rule out 2.
Second deduction: what changes in B?
After placing 2 in A, row 1 is missing 1 and 5. Column 1 contains 4, 5, 3 and 6, ruling out 5. B must be 1. Its box already contains 2, 3, 4, 5 and 6, confirming that 1 fits.
Now try R1C5, the last empty cell in that row. Which number is missing?
Check the third step
The missing number is 5. Column 5 contains 2, 6, 1 and 4; the top-right box contains 4, 6, 1, 2 and 3. Neither rules out 5. The completed first row is 1, 2, 3, 4, 5, 6. You have connected three deductions without guessing.
A routine for deciding where to look
- Find an area with few empty cells. It might be a row, column, or box. The more numbers already placed, the fewer possibilities you need to compare.
- List what is missing. Then check which numbers the other two crossing areas rule out for each cell.
- Write only when you can explain why. “This row needs a 4, and no other number fits here” is a deduction. “I’ll try a 4” is a guess.
How to use a hint without losing the challenge
Before looking at the complete solution, try to get a smaller nudge: the area to inspect or the number worth focusing on. Return to the grid and work through the reasoning yourself.
When to move to a larger sudoku
Once the rules feel familiar, try a 6×6 grid using numbers 1 through 6 and boxes that are two rows by three columns, or three rows by two columns, depending on the layout. Then move to 9×9 with 3×3 boxes. The no-repeats rule stays the same; there is simply more information to observe.
Grid size alone does not determine difficulty. The point of this progression is to get comfortable with the rules before facing a board with more cells.
For a next step, explore how to note and update candidates, or see six common mistakes and how to correct them.
Reading path: Start with sudoku
Keep exploring this topic
- How to Mark Sudoku Candidates, Step by Step
Learn how to find the possible numbers for a cell, when to erase a candidate, and why a possibility is not yet an answer.
- 6 Common Sudoku Mistakes and How to Fix Them
Repeated numbers or a cell with no candidates do not mean you must start over. Check six common mistakes and learn how to resume carefully.