What makes a nonogram easy or hard
"Difficulty" in a nonogram isn't just about how big the grid is. A 20×20 can fall out almost by itself, while a 10×10 can make you work for every square. What really sets the difficulty is how deep you have to reason to find the next forced move. This guide breaks down what actually drives it — and shares a surprising finding from the research on how rarely a fair puzzle needs anything clever at all.
Size is only part of it
A bigger grid does mean more lines to track and more cross-checking, so large puzzles take longer. But length alone doesn't make a line hard — a 20-wide row with a single big run is trivial, while a short row packed with small runs and tight gaps can need real thought. Size affects how long a puzzle takes far more than how hard each step is.
It's really about how deep the deductions go
The truest measure of difficulty is what kind of reasoning the puzzle demands. The easiest puzzles are "line-solvable": you can finish them by looking at one row or column at a time, filling whatever that single line forces, and never needing to hold two lines in your head at once. Most gentle puzzles are exactly this.
Harder puzzles need you to combine information — to notice that a square's state only becomes forced once you consider a row and a column together, or a small cluster of lines at once. The deeper that combination has to go before the next square is forced, the harder the puzzle feels, regardless of its size.
What the research says about guessing
Here's the reassuring part. Academic work on nonogram solving (Batenburg and Kosters, 2012) measured how much reasoning uniquely-solvable puzzles actually require. Beyond simple line-by-line solving, the next step up is a well-defined, still-deterministic technique — combining pairs of lines — and their exhaustive enumeration found that 93.8–95.5% of the non-simple puzzles are solvable by exactly that, with no guessing at all.
Even more striking: only about 0.06–0.14% of all uniquely-solvable puzzles need anything beyond that pair-of-lines reasoning. In other words, the overwhelming majority of well-formed nonograms — including every hard one you'll meet in normal play — can be solved by pure, bounded logic. Genuine trial-and-error is vanishingly rare in a fair puzzle, which is why "never guess" is such reliable advice.
Density and shape matter too
Beyond deduction depth, a couple of surface features nudge the difficulty. Very sparse pictures (mostly empty) and very dense ones (mostly filled) tend to be easier, because the extremes give lots of forced squares early. The trickiest puzzles usually sit in the middle, with a balanced mix of filled and empty and plenty of short, broken-up runs that resist the quick opening moves. A clean, recognizable subject also helps a solver stay oriented, even if it doesn't change the underlying logic.
How we label easy, medium, and hard
On this site, a puzzle's rating comes from how deep its solving reasoning goes, combined with shape statistics like how filled the grid is. Line-solvable puzzles land in easy; ones that need real cross-line combination move toward hard; anything that would require guessing is rejected outright rather than published. The full pipeline is described on the "how we make our nonograms" page — but the short version is that difficulty here is measured, not guessed.