How Nonograms Work

Summary:
A nonogram is a picture logic puzzle: the numbers beside each row and above each column give the lengths of the blocks of filled cells in that line, in order, and when every clue is satisfied a black-and-white picture appears. To solve one, you fill or rule out one cell at a time, each time because the clues leave no other choice.

Want to make your own? Nonogram generates nonogram puzzles with matching answer keys, ready for print.

Overview

Nonograms are also called picross, griddlers and hanjie. You start with an empty grid. Each row has a list of numbers to its left and each column has a list above it. Those numbers describe the blocks of filled cells in that line. Fill the cells the clues require, leave the rest empty, and a picture appears.

This 10×10 puzzle is the example used throughout this page. Rows are numbered 1 to 10 from the top and columns 1 to 10 from the left.

The Goal

Fill the grid so that every row and every column matches its clues exactly. Any cell that no clue asks for stays empty. When you are done, the filled cells form the picture.

The Rules

1. Each number is a run. A 4 means four filled cells next to each other in that line, with nothing between them.
2. Runs appear in order. A row’s clues read left to right and a column’s clues read top to bottom, in the same order as the runs on the grid.
3. Runs need a gap. Two runs in the same line are separated by at least one empty cell. Row 1’s 2 2 is two separate blocks of two, never one block of four.
4. The gaps can be any size. The clue does not say how many empty cells sit before, between or after the runs, only that there is at least one between runs.
5. No number means no filled cells. A line without a clue (some puzzles print a 0 instead) is empty from end to end. Row 10 in the example has no clue.

How to Start Solving

Mark every cell you know is empty with a small ✕, so you never fill it by mistake. Then work through these moves. Together they solve the whole example, one certain cell at a time.

1. Fill the lines that fit exactly

Add up the runs in a line and add one cell for each gap between them. If the total equals the line length, there is only one way to place the runs. Rows 3, 4 and 5 each read 10 in a line of ten cells, so all three rows are completely filled. Row 10 has no clue, so all ten of its cells get an ✕.

2. Overlap the runs that cannot move far

When a line does not fit exactly, count its slack: the line length minus the runs and the minimum gaps. A run can only slide that many cells, so any run longer than the slack has cells that are filled wherever it sits: its length minus the slack, in the middle of its possible range. Row 6 reads 8: 10 − 8 leaves a slack of 2, so 8 − 2 = 6 cells are certain, columns 3 to 8. Row 2 reads 4 4: 4 + 1 + 4 = 9 leaves a slack of 1, so 3 cells of each run are certain: columns 2 to 4 and columns 7 to 9.

3. Rule out the cells a run cannot reach

Column 1 reads 4, and rows 3, 4 and 5 are already filled in it. A run of four that contains those three cells can only sit in rows 2 to 5 or rows 3 to 6, so rows 1, 7, 8 and 9 of column 1 are empty. Column 10 also reads 4, and the same reasoning rules out the same four cells there.

4. Let the columns finish a row

Columns 3 to 8 each read 7. In column 3, rows 2 to 6 are now filled, five cells in a row, so the run of seven must start in row 1 or row 2, and either way it reaches row 7. Columns 4, 7 and 8 work the same way. In columns 5 and 6 only rows 3 to 6 are filled so far, so the run of seven, which must include those four cells, starts in row 1, 2 or 3; every one of those positions still reaches row 7. That puts six filled cells in row 7, columns 3 to 8, which is exactly its clue of 6. Row 7 is finished, so its other four cells get an ✕.

5. Use what the finished line tells its neighbours

Column 2 reads 6. Rows 2 to 5 are filled in it and row 7 is now empty, so the run can only be rows 1 to 6: fill row 1 and row 6 of column 2, and mark rows 8 and 9 empty. Column 9 is the mirror image and works out the same way.

6. Anchor a run against an empty cell

Row 1 reads 2 2. Column 2 is filled and column 1 is empty. The filled cell must belong to the first run, because the second run has to sit to the right of the first, so the first run starts at column 2 and covers columns 2 and 3. In the same way, column 9 is filled and column 10 is empty, so the second run covers columns 8 and 9. Row 1 is finished; the rest of it is empty.

7. Keep alternating until the picture appears

Every cell you place gives the crossing line new information, so keep switching between rows and columns:

• Column 3 now has row 1 filled, so its run of seven is rows 1 to 7 and row 8 is empty. Column 8 is the same.
• Row 8 reads 4, and columns 1, 2, 3, 8, 9 and 10 are empty in it, so the run fills columns 4 to 7 exactly.
• Columns 4 and 7 now have rows 2 to 8 filled, which is their full 7, so row 9 is empty there. Row 9’s 2 must be columns 5 and 6.
• Column 5’s run of seven now ends at row 9, so it is rows 3 to 9 and row 2 is empty. Column 6 is the mirror image, so row 2 is empty in columns 5 and 6. That pins row 2’s first run to columns 1 to 4 and the second run to columns 7 to 10.
• Column 1 now has row 2 filled, so its run is rows 2 to 5 and row 6 is empty. Column 10 is the same, so row 6’s 8 fills columns 2 to 9.

Every clue is now satisfied, and the picture is complete.

Common Mistakes

• Joining two runs. A 2 2 clue is two blocks with at least one empty cell between them. If your two blocks touch, they read as a single 4.
• Forgetting the order. In a row, the first number is the leftmost run. A row of 1 3 cannot have the three-cell run on the left.
• Guessing too early. If no line seems to give you a certain cell, look again for an overlap, an anchored run or a finished clue. Puzzles like this one are solved entirely by these moves.
• Not marking empty cells. An ✕ is information. Lines often unlock only after you mark the cells a run cannot reach.

Bigger Pictures

Nonograms range from small teaching boards like this one to large grids with fine detail. Most big puzzles yield to the same moves: exact fits, overlaps, ruled-out cells and finished lines. They just take longer, and the picture is more detailed when it appears. Start with the longest runs and the lines with the least slack; they give the first certain cells.

Outcome

You now know how nonograms work: each number is a run of filled cells, runs appear in order, runs in the same line are separated by at least one empty cell, and a line without a clue stays empty. You can fill exact fits, overlap runs using the slack, rule out the cells a run cannot reach, anchor a run against an empty cell, and finish a line once its clue is complete.

Try It Online

Solving in the browser works like pencil and paper: click a cell to fill it, click it again to mark it with an ✕, and click once more to clear it. Drag from an empty cell to fill a whole run in one stroke, and right-click to put an ✕ on a cell or take it off. Play Nonogram online, and see How to Play Puzzles Online for the general controls such as Check and Reset.

FAQ

What is a nonogram?
A nonogram is a logic puzzle where number clues tell you how many cells to fill in each row and column. It is also known as picross, griddlers or hanjie. Solving every clue reveals a picture.

What do the numbers in a nonogram mean?
Each number is a block of filled cells in that line. A row reading 3 1 has a block of three filled cells, then at least one empty cell, then a single filled cell.

How do you solve a nonogram?
Fill the lines whose clues fit exactly, overlap the long runs, mark the cells no run can reach with an ✕, and keep switching between rows and columns. Each move above uses only the clues and the cells already decided.

Are picross, griddlers and nonograms the same thing?
Yes. Picross, griddlers and hanjie are all names for the same puzzle.

Do I have to guess to solve a nonogram?
Usually not. Most well-made nonograms, including the example on this page, can be solved one certain cell at a time by comparing the clues with what is already on the grid.

Can a nonogram have more than one solution?
Some picture puzzles can, which is why good puzzles are checked for a single answer. When you play online, Check accepts any filling that matches every clue, so a correct solve is never marked wrong.

Further Reading

• How to Create Nonogram Puzzles in Puzzle Maker Pro
• How to Play Puzzles Online
• How Color Nonograms Work

Make Your Own Nonogram Puzzles

Now that you know how the clues fit together, turn your own pictures into nonograms, each with its answer key, ready for a puzzle book or a printable worksheet.

Create your own nonogram puzzles with Nonogram

Not ready yet? Try the free demo first — it covers every module.