A nonogram, also called picross or griddlers, is a logic puzzle where number clues tell you which squares in a grid to fill. Every solvable nonogram can be finished by reasoning alone, with no guessing, once you know a handful of techniques. This guide explains how to read the clues, then walks through the techniques in the order you will use them, with worked examples you can check against a real grid.
The numbers beside each row and above each column give the lengths of the runs of filled squares in that line, in order. A clue of 3 1 means there is a run of three filled squares, then at least one empty square, then a single filled square, and nothing else in that line is filled.
A single 0 or a blank means the whole line is empty. Two runs are always separated by at least one empty square, which is the fact most of the techniques below depend on.
Add the runs together and add one gap between each pair. If that total equals the length of the line, the line has no slack and you can fill it completely.
A clue of 3 1 in a 5-square line needs 3 + 1 + 1 = 5 squares, so the answer is filled, filled, filled, empty, filled.
A clue of 7 2 in a 10-square line needs 7 + 1 + 2 = 10 squares, so it is 7 filled, one empty, 2 filled.
A clue of 1 1 1 in a 5-square line is filled, empty, filled, empty, filled.
Always scan for these first. They give you a skeleton to work from on every other line.
When a line has some slack, a long run still has squares it must cover wherever it sits. Slide the run to the far left, then to the far right. Any square filled in both positions is certain.
The slack is the line length minus the minimum space the clue needs. A run longer than the slack always leaves a certain core of its length minus the slack:
Do this for the first run from the left edge and the last run from the right edge in lines with several runs; the same logic applies to each run within its own possible range.
| Line length | Clue | Slack | Certain filled squares |
|---|---|---|---|
| 10 | 8 | 2 | Squares 3 to 8 (six squares) |
| 5 | 4 | 1 | Squares 2 to 4 (three squares) |
| 10 | 6 | 4 | Squares 5 and 6 (two squares) |
| 10 | 5 | 5 | None: the run has no certain square |
Mark squares you have proved empty with a cross. Crosses are not part of the answer; they are notes, and they are what make the next steps possible. In our nonogram game use the Cross out tool, or right-click, to place them.
Typical places to cross out:
Squares a run can never reach, for example more than a run's length away from a filled square that belongs to it.
The square immediately after a completed run, since runs need a gap.
Every remaining square in a line once all its runs are placed.
In the game a clue turns grey when its line matches, which is a quick way to see which lines are done.
If a filled square touches the edge of the grid and the first clue is the run it must belong to, you can fill the rest of that run from the edge. For a first clue of 4 with a filled square in position 1, positions 1 to 4 are filled and position 5 is empty.
The same works in the middle. If a filled square is already known to belong to a run of length 3, and it has an empty square on one side, the run must extend the other way.
Every square belongs to a row and a column. A square you have solved in one direction becomes a fixed clue for the other. Alternate between rows and columns; solving a column often unlocks a row that looked stuck.
Work the lines with the biggest numbers first, since they have the least slack, and leave short, sparse lines for later when more squares are known.
Re-read every line with new crosses on it; a gap you added may now split a run's possible positions.
Check each clue's leftmost and rightmost placement again, using the new filled squares and crosses as limits.
Look at runs next to a cross: a cross can force a run to start or end there.
If a line seems impossible, one earlier mark is wrong. Find the contradiction and undo it.
A well-made nonogram never needs guessing. Our generator only keeps a puzzle if a line-by-line solver can finish it without a guess, so if you feel forced to guess, there is a clue you have not used yet.
Start with a 5x5 grid, where overlap and exact fits will solve most of it, then move to 10x10, which needs the crossing-line technique, and finally 15x15 for a long sit-down session. You can set the size in the nonogram game, and the best time for each size is saved in your browser.
For more puzzle types and general strategy, see how to solve logic puzzles, logic puzzle tips and the logic games hub. Another grid puzzle with a similar feel is Hitori.
A nonogram is a grid puzzle in which the numbers beside each row and above each column give the lengths of the runs of filled squares in that line. Filling the grid to match every clue reveals a picture or pattern. It is also called picross or griddlers.
Look for lines where the clue plus its gaps equals the line length, and fill those completely. Then use the overlap method on lines with a long run to find certain squares, and cross out squares that cannot be filled. Alternate between rows and columns.
Not in a well-made one. Every puzzle should have a single solution reachable by logic. If you feel forced to guess, re-check the leftmost and rightmost positions of each run against your new filled squares and crosses.
Place a run as far left as it can go, then as far right. Any squares filled in both positions are certain. For an 8 in a 10-square line, squares 3 to 8 are filled in both, so you can fill them straight away.
It varies with experience and the puzzle. Beginners often need several minutes, and times drop with practice as the techniques become automatic. Our game saves your best time for each grid size so you can track your own progress.
Nonograms reward patience and a small set of repeatable techniques. Learn the exact fit and the overlap method, keep your crosses tidy, and alternate between rows and columns. Then try a fresh puzzle in the nonogram game and see how far logic alone takes you.