How to Read Nonogram Clues
Reading the clues right is the one skill that separates solvers who finish from solvers who get stuck. A number is the length of one run of filled squares, and the order never changes.
One number
One number, one block. A row marked 4 has four filled squares side by side, and nothing else filled in that row.
The block can sit anywhere it fits. In a nine-wide row, a block of four can start at square 1, 2, 3, 4, 5, or 6.
Several numbers
Several numbers, several blocks, read in order. A row marked 2 1 3 has a block of two, then a block of one, then a block of three.
Two things trip people up here:
- The order can't change. 3 1 and 1 3 are not the same row.
- Gaps are at least one square, but can be more. The clues give block sizes, never gap sizes.
Work out a line's minimum length
Before you place anything, add it up: blocks plus one empty square for each gap between them.
For 2 3, the blocks total five squares and there's one gap, so the minimum length is six. In an eight-wide row, only two squares of slack remain. Tight lines like that are usually the fastest way into a puzzle.
Notation to remember: minimum length = sum of blocks + (number of blocks − 1)
When the clue fills the whole line
If the minimum length equals the width, the whole line is fixed and you can draw it right now. In a five-wide row, 5 fills every square. 2 2 in five wide fills squares 1, 2, 4, and 5, with square 3 empty.
The 0 clue
0 means the line is completely empty. Mark every square and move on. It looks trivial, but it constrains every column that crosses it.
Three worked examples
Example 1, the forced middle. A ten-wide row with the single clue 6. The block can start at square 1 through 5. In every position, squares 5 and 6 are filled. So both are certain.
Example 2, no room to move. A seven-wide row with 3 3. Minimum length is seven, same as the row. No slack: squares 1–3 filled, square 4 empty, squares 5–7 filled.
Example 3, the gap is forced. A five-wide column with 1 1 1. Minimum length is five. The pattern has to be filled, empty, filled, empty, filled.
Four common misreadings
- Reading 1 1 as two touching squares.
- Assuming the gap is exactly one square.
- Assuming a block must touch the edge.
- Reading rows only, and ignoring the columns.
Quick answers
What do the numbers mean?
Each one is the length of a run of filled squares. Several numbers mean several runs, in the printed order, with at least one empty square between them.
What if a row has no numbers?
Some versions print a 0 to make it clear. Either way, the row is empty.
How do I know where a block starts?
You usually don't at first. You narrow it down until the block has only one legal spot, using row and column clues together.
Do longer clues make a puzzle easier?
Often yes, because they leave fewer legal spots. A big, sparse clue set can be harder than a dense one.
Try it on a real grid
Clue reading becomes automatic after a few puzzles. Try a free 5×5 Nonogram
Next, read the complete rules for beginners, or go straight to the technique that uses clue lengths best: the overlap method. Ready for more? Try a 15×15 puzzle.