Stepping up from 4x4 to 6x6 grids, one drop at a time
Learn how to move from a 4x4 to 6x6 number grid, checking rows, columns and 2x3 boxes one at a time.
A solver looks at a 4x4 board where the third row reads 2, 4, 1 and one empty cell. The row needs a 3, so the solver checks the column above that cell and the 2x2 box around it. Neither the column nor the box holds a 3 yet, so the solver places the number and keeps going across the board.
A 6x6 board has six rows, six columns and the numbers 1 through 6. The boxes are 2x3, two cells tall and three cells wide, which gives each box six cells and gives the board six boxes. At the start, more cells are empty, and the solver checks two kinds of regions: the rows and columns, and the boxes.
Nothing about the rule has changed. Every row, column and box contains every number one time. The Classic 6x6 set in NumFall on the App Store has 100 levels, and the first ones use this same rule on the larger grid.
Reading a 6x6 board one row and one box at a time
A solver starts with one row. Picture a row that holds 1, 4 and 6, with three cells still empty. The solver notes that the row already holds 1, 4 and 6, which leaves 2, 3 and 5 as the only options for the three empty cells.
Next, the solver checks the column that runs through one of those cells. Say that column holds 2 and 5 higher up. 3 is the only one of those three numbers still open for that cell, so the candidate is 3.
The third check looks at the 2x3 box that surrounds the cell. The solver looks at the six cells that sit together in a box, two tall and three wide, and notes the numbers they hold. A 3 in a neighboring cell of the box rules out the candidate, so the cell stays empty for now. When the box holds no 3, all three checks agree.
Solvers who record each unit in turn, row first, then column, then box, tend to make fewer mistakes than those who check by eye. Writing a short note beside the board helps, for example: "row: 1 4 6, column: 2 5, box: 4 6."
The solver places a value in a cell only when the row, column and box all agree. The cell stays blank until then, and the notes stay on the page.
Keeping the drop order in view on a larger board
A solver who fills the board by dropping numbers into columns meets a rule that a paper grid does not have: a number falls to the lowest empty cell in the column it is dropped into. The solver does not choose the row. Which cell each number lands in depends on the order of the drops, so the final grid changes with that order.
Consider a column whose bottom two cells are empty, with a 5 and a 2 still to place. Dropping the 5 first puts it in the bottom cell, with the 2 resting above it. Drop the 2 first and the two numbers switch places. Only one of those orders works when the bottom row needs a 5.
A solver can write out two drop orders on a pencil sheet and trace each one down the columns. Each order gets a separate small grid, and the landing cell is marked after each drop. The solver checks rows, columns and boxes on both sheets and keeps the order that leaves no repeated number.
On a 6x6 board, the main risk is an early drop that fills a cell a later row needs. Once the number sits there, the cell is locked, and the solver may not see the conflict until several more drops later.
A short practice routine for the first Classic 6x6 levels
Pick one Classic 6x6 level and follow the same routine each time. Classic 6x6 levels are timed, and three stars go to fast finishes with no mistakes, so a solver can start a clock and keep it running from the first drop to the last.
- Scan the six rows from top to bottom, then the six columns from left to right, then the six boxes from top left to bottom right.
- Use that same order on every pass so no region gets skipped by accident.
- Write candidates only for cells with two or fewer options. Cells with three or more candidates stay blank, which keeps the page readable.
- Fill a cell only when the row, the column and the box all agree, and cross out the candidates it removes from neighboring cells.
After the level ends, the solver records the finishing time and counts the mistakes. On the pencil sheet, a small mark beside each box shows which one was checked first, and the next level starts with a different box.
FAQ
How do you check a 6x6 number grid one row at a time?
Start with one row and write down the numbers it already holds. The empty cells in that row can only take the numbers that are missing from it. Then check the column and the 2x3 box for each candidate before placing it.
What size are the boxes on a 6x6 grid?
Each box on a 6x6 grid is two cells tall and three cells wide, so it holds six cells. That gives the board six boxes, and each box must hold the numbers 1 through 6 once.
Why does the order of drops matter when filling a 6x6 grid?
A dropped number falls to the lowest empty cell in its column, so the drop order decides the final layout. A beginner who drops a number too early can fill a cell that a later row needs.
Can a beginner practice 4x4 to 6x6 grids in a timed mode?
Its levels are timed, and three stars go to fast finishes with no mistakes.
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