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Nonograms: the rules and how to solve them
A nonogram is a grid in which you black out cells according to the numbers at the end of each row and column: each number gives, in order, the length of a block of black cells. It is also known as griddlers, hanjie or paint by numbers, and as Picross at Nintendo.
On Neurostim, Inkgrid draws one grid per size every day, the same for everyone, and each one can be solved line by line without any trial and error. This guide gives the rules, the controls, the method with diagrams and benchmarks measured on 1,500 grids.
In short
- Genre: a single-player logic puzzle against the clock.
- Goal: black out exactly the cells that the numbers of every row and column call for.
- Sizes: Easy 5 × 5, Medium 10 × 10, Hard 15 × 15.
- Daily challenge: one grid per size, the same for everyone, renewed at midnight, Paris time. Your first try is ranked.
- Free run: a new grid every game, your best time of the day is ranked.
- No trial and error: a program limited to line logic has solved each grid before you get it.
- Account: not needed, a guest name is enough to be ranked.
- Devices: computer, with a mouse or the keyboard, and phone or tablet, by touch.
The rules of nonograms
Reading the numbers
Each row and column has a list of numbers. Each number stands for a block of consecutive black cells. The blocks come in the order of the numbers, left to right on a row, top to bottom on a column. All other cells stay white.
Edge cases
- Between two blocks there is at least one white cell, sometimes more. Without it, they would be one block.
- A block can touch the edge of the grid.
- A 0 means the line is entirely white.
- The numbers do not say where a block starts: working that out is the whole method.
- You win when every number is met. Crosses do not count: they are notes for you.
In the diagrams on this page:
- a black cell
- a certain white cell, marked with a cross
- a cell still unknown
- the cell the text is talking about
- a number of the row or column
Solving a nonogram line by line
A line's slack
This is the basic tool. Add up the blocks of a line, add one cell for each required gap between them, and subtract the total from the length of the line: that gives you its slack, the number of cells its blocks can slide. Any block longer than the slack has certain cells, as many as its length minus the slack, where its extreme positions overlap.
A block of 7 on 10 cells has a slack of 3: it must cover 7 minus 3, so 4 cells, the middle ones.
Several blocks
With 3 and 4 on 10 cells, the total is 3 + 1 + 4 = 8, and the slack is 2. The block of 3 gives one certain cell, the third; the block of 4 gives two, the seventh and eighth. Push all the blocks as far left as they go, then as far right: the certain cells are where the same block overlaps itself.
Lines with no slack
When the total equals the length, everything is settled: 2, 3 and 3 on 10 cells make 2 + 1 + 3 + 1 + 3 = 10. The line fills up in one go, crosses included.
Crosses
A cross is worth as much as a black cell. A cell no block can reach is white. With a single block of 2 and a black cell in the centre of a line of 5, both ends are out of reach.
A cross also cuts a line into pieces. Here, a cross on the fourth cell leaves three cells on the left, too few for a block of 4: that gives three more crosses. Six cells remain on the right, so the slack is 2 and two cells are certain, the seventh and eighth.
The edge anchors blocks
A black cell against the edge belongs to the first block, which therefore starts there. With 3 and 2, a black left-hand cell gives the whole block of 3 and the cross after it.
It also works close to the edge: with 3 and 1, a black cell in second position can only belong to the block of 3, which starts on the first or second cell. So the third cell is black either way.
Crossing rows and columns
Every cell you find helps the row and the column running through it. Here is a small complete grid: from top to bottom, the rows ask for 1 1, 5, 5, 3 and 1; from left to right, the columns ask for 2, 4, 4, 4 and 2. The two rows marked 5 fill up at once.
The columns marked 2 have their block: the rest of those columns is white. The three middle columns have a slack of 1, so three certain cells each, which blacks out three cells of the fourth row and finishes its 3.
The first row still has to place 1 and 1 in three cells: that means the second and fourth, with a cross between them. The middle column has lost its first cell, so its block of 4 runs down to the bottom. The last 1 is found, and a heart appears.
When nothing moves
On a hard nonogram elsewhere, you may have to assume a value for one cell and follow it through to a contradiction, or reason over several lines at once. On Inkgrid you will not need to: if you are stuck, some row or column still has a cell to give. Go back over the lines that have changed since you last read them.
Getting faster
- Work out the slack in your head, then skip the loose lines. The table further down shows when a line is not worth reading early on.
- Make one full first pass. Read all the rows, then all the columns, without lingering: that is where the biggest share of cells falls.
- Reread only what has changed. A line with no new cell or cross has nothing more to tell you.
- Mark the crosses that help. They do not count when you send the grid, but they shrink the slack. Place the ones that split a line and skip those on a finished line.
- Drag instead of clicking. A single stroke places a whole block. On touch screens, keep the "Cross" tool for moments when you place several in a row.
- Do not trust the grey. On 15 × 15, with nearly four small blocks per line, blocks of the right lengths in the wrong place are an easy mistake to make.
If you want the clock on other grids, takuzu and sudoku call for the same kind of reading, and minesweeper also has you deduce from numbers.
Benchmarks: slack, blocks and rejected grids
What a first reading gives you
Across 1,500 pictures drawn by Inkgrid's generator in November 2026 (500 per size), we had the game's real solver read each row and column on the empty grid.
| 5 × 5 | 10 × 10 | 15 × 15 | |
|---|---|---|---|
| Rows and columns giving at least one cell | 72.3% | 60.3% | 51.1% |
| Cells known after that first reading | 67.2% | 49.7% | 28.4% |
| Share of black cells | 62.2% | 61.7% | 57.3% |
| Blocks per line, on average | 1.11 | 1.66 | 3.99 |
| Average block length | 2.81 | 3.71 | 2.15 |
| Solver round trips, in the middle of the series | 2 | 2 | 4 |
| Solver round trips, at most | 3 | 6 | 14 |
A round trip is one reading of all the rows and then all the columns. So a 15 × 15 is not just a bigger 10 × 10: its blocks are short and numerous, the first reading gives only just over a quarter of the cells, and you have to come back to lines far more often.
When a line is worth reading
Here is the share of lines that give at least one cell on the empty grid, by slack.
| Slack | 0 or 1 | 2 | 3 | 4 | 5 | 6 or more |
|---|---|---|---|---|---|---|
| 10 × 10 | 99.9% or more | 98.2% | 71.0% | 33.3% | 0% | 0% |
| 15 × 15 | 100% | 90.7% | 56.8% | 24.9% | 8.0% | 1.4% or less |
Remember it this way: up to a slack of 2, read the line; from 5 on, skip it. On 15 × 15, lines with a slack of 5 or more make up over a quarter of all lines (26.7%), so do not spend time on them during the first pass.
How many grids are thrown out
Not every random grid can be solved without trial and error. Over 1,000 raw draws per size, the line-only solver finishes 94.6% on 5 × 5, 86.5% on 10 × 10 and 68.4% on 15 × 15; the others are discarded. The generator also rejects grids solved too quickly, so it draws 1.6 grids on average on 5 × 5, 1.1 on 10 × 10 and 2.5 on 15 × 15 to keep one. Jan Wolter tested larger: of 5,000 random 30 × 30 grids, 97.5% have several solutions and only 0.4% can be solved one line at a time.
What about records?
We found no reference world table for nonograms. To see where you stand, take a shared grid: the one on the daily leaderboard.
The history of nonograms
- 1987: Japanese graphics editor Non Ishida wins a competition in Tokyo with a picture made of the lit windows of a skyscraper.
- 1988: she publishes three "Window Art Puzzles" in Japan. Tetsuya Nishio publishes the same type of grid in another magazine at about the same time.
- 1989: British puzzle collector James Dalgety teams up with Non Ishida to take the game outside Japan.
- 1990: Dalgety coins the word nonogram, from "Non" and "diagram", and The Sunday Telegraph runs the grids weekly. With Bill Stanton, he writes what may be the first solving program, designed to use only human logic.
- 1995: Nintendo releases Mario's Picross on the Game Boy, on 14 March in Japan. The game sells well in Japan and poorly elsewhere. Picross is a Nintendo trademark, from picture crossword.
- 1996: Ueda and Nagao show that the nonogram problem is NP-complete.
- 1998: readers of The Sunday Telegraph pick the name Griddler in a competition. The Puzzle Museum lists Griddler and Nonogram as registered trademarks.
Inkgrid has no history of its own to tell: it takes the rules of the genre and, like Dalgety and Stanton's program, only keeps grids that human logic can finish.
Frequently asked questions
What is a nonogram?
A nonogram is a logic puzzle where you black out cells according to numbers placed at the end of the rows and columns. Each number gives the length of a block of black cells, in order. It was born in Japan in the late 1980s and often reveals a drawing once finished.
How do you play a nonogram?
Read the numbers at the end of each line: each stands for a block of consecutive black cells, in that order, with at least one white cell between two blocks. Black out the cells you are certain of, mark the others with a cross, and finish when every row and column matches.
How do you solve a nonogram step by step?
First work out each line's slack, which is its length minus its blocks and their gaps. Any block longer than the slack has certain cells. Carry those cells over to the crossing lines, mark the impossible cells with a cross, and start again on whatever has changed until the grid is done.
How do you solve hard nonograms with small numbers?
Do not look for big blocks straight away: on 15 × 15 they are rare. Read the lines with a slack of 2 or less, which nearly always give a cell, then return to each line that has changed. On our grids, four round trips were enough at least half the time.
Is every nonogram solvable?
Not every grid has a single answer: random grids often allow several solutions, and many cannot be solved one line at a time. Well-made puzzles are checked for this. On Inkgrid, the generator keeps only grids its line solver can finish, which means a single solution and no guessing.
Is a nonogram harder than sudoku?
Neither is harder in general, and both are NP-complete problems once grids can grow to any size. They differ in effort: sudoku asks you to spot techniques on one 9 × 9 grid, while a nonogram asks you to reread many lines. Our sudoku guide shows what its hardest grids demand.
Are nonograms Japanese?
Yes, nonograms come from Japan: Non Ishida and Tetsuya Nishio published the first ones independently around 1988. The name, though, was coined in Britain in 1990 by James Dalgety, from "Non" and "diagram". The puzzle carries many other names too, such as griddlers, hanjie and Picross.
What is the difference between a nonogram and Picross?
There is none in the rules: they are the same puzzle. Nonogram is the generic name, griddlers comes from The Sunday Telegraph, hanjie and paint by numbers are other common names, and Picross is a Nintendo trademark, from picture crossword. Inkgrid is simply the name of our version.
Why are nonograms so hard?
They get hard because each line gives little on its own and you have to keep crossing rows with columns. On a 15 × 15 from our generator, reading each line alone on the empty grid reveals only 28.4% of the cells, and lines average nearly four short blocks, so the deductions come slowly at first.
What is the nonogram world record?
We found no reference world table for nonogram times, and a time only means something on a given grid. The fairest way to compare yourself is to play the same grid as everyone else, which is the point of Inkgrid's daily challenge and of its leaderboard.
Can you play nonograms for free online?
Yes, Inkgrid is free and runs in your browser, with nothing to install and no sign-up: start the clock and you are ranked under a guest name. The daily grid changes at midnight, Paris time, and the free run provides more of them, up to the daily limit.
Sources
- Wikipedia, Nonogram and Mario's Picross, checked on 7 November 2026.
- Wikipedia (French), Nonogramme, checked on 7 November 2026.
- The Puzzle Museum, the history of griddlers, checked on 7 November 2026.
- Jan Wolter, Survey of Paint-by-Number Puzzle Solvers, checked on 7 November 2026.
Your turn
Today's Inkgrid challenge is the same for everyone until midnight, Paris time. No account needed: you get a guest name with your first game.
Games of the same kind
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