Flowchart Symbols and Their Meanings: The Complete Guide
The shapes in a flowchart are a shared language. Learn what each one means and your diagrams become instantly readable to anyone who knows the same vocabulary.
Flowchart symbols are not decoration. Each shape carries a specific meaning, and that meaning is standardized enough that someone who has never seen your particular diagram can still read it correctly. A diamond always means a decision. A rectangle always means an action. When you respect these conventions, your flowchart communicates without a legend. When you invent your own meanings, you force every reader to guess, and the whole advantage of a flowchart evaporates.
Most of these conventions trace back to the ANSI and later ISO standards for flowcharting, refined over decades in engineering and computing. You do not need to memorize the entire catalogue - a working diagrammer uses perhaps six or seven shapes regularly - but knowing the full set means you will recognize any flowchart you encounter and can reach for the exact symbol a situation calls for. This guide covers each one, what it means, and the mistakes people make with it.
The core process symbols
These are the symbols you will use in almost every flowchart. If you learn nothing else, learn these four, because together they can express the vast majority of processes you will ever need to map.
- Terminator (oval or stadium shape): marks the start or end of a process. Labelled "Start", "End", "Begin", or the specific trigger like "Order received".
- Process (rectangle): a single action or operation - "calculate total", "send email", "update record". The most common shape in any flowchart.
- Decision (diamond): a branching point with a question inside. Every arrow leaving it must be labelled with the condition, such as "Yes"/"No" or "In stock"/"Out of stock".
- Flow line (arrow): connects symbols and shows direction. The backbone that turns a set of shapes into a process.
- Input/Output (parallelogram): data entering or leaving the process - a keyboard entry, a report, a form, a printout.
- Predefined process (rectangle with double side bars): a sub-process defined in detail elsewhere, keeping the main diagram uncluttered.
- Document (rectangle with a wavy bottom edge): a printed or generated document, like an invoice or a contract.
- Connector (small circle): joins flow lines across the page or to another part of the diagram without crossing arrows.
Data, storage, and specialized symbols
Beyond the core set, flowcharts have symbols for representing where data lives and how it moves, inherited largely from the era when flowcharts documented computer programs and their storage media. You will meet these most often in technical or data-flow contexts. A cylinder represents a database or stored data - think of it as the shape of a physical disk platter stack, which is where the convention comes from. A shape like a rectangle with a curved bottom represents magnetic or internal storage.
Other specialized symbols include the manual input shape (a rectangle with a slanted top, for data typed by a person), the manual operation shape (a trapezoid, for a step done by hand rather than automatically), and the delay symbol (a shape like a capsule cut in half, marking a waiting period in the process). The preparation shape, a hexagon, marks a setup or initialization step, such as setting a counter to zero before a loop begins.
You will rarely need all of these in one diagram, and using too many obscure symbols can make a flowchart harder to read, not easier. The rule of thumb: use a specialized symbol only when its specific meaning adds clarity that a plain rectangle would lose. If a reader would have to consult a legend to understand the shape, a labelled rectangle is often the better choice.
Connectors, branches, and merging paths
As flowcharts grow, keeping flow lines from crossing becomes a real challenge, and this is where connector symbols earn their place. An on-page connector, drawn as a small labelled circle, lets you break a long arrow and pick it up elsewhere on the same page - you put a circle labelled "A" where the flow leaves and another circle labelled "A" where it resumes. An off-page connector, usually a pentagon or home-plate shape, does the same thing across pages or across linked diagrams.
Merging is the counterpart to branching. When two paths that split earlier need to rejoin, the arrows simply point into the same next shape. You do not need a special merge symbol in standard flowcharting - a decision diamond handles the split and a shared target handles the join. Some notations use a small circle as an explicit merge point, which can help readability when many arrows converge, but it is optional.
Common symbol mistakes to avoid
The single most common error is using a rectangle where a diamond belongs. If a step has more than one arrow leaving it based on a condition, it is a decision and needs a diamond. Squeezing a yes/no question into a rectangle and drawing two arrows out of it breaks the visual grammar and readers will misread it. Conversely, do not use a diamond for a step that always leads to the same next step - that is just a process.
The second frequent mistake is leaving decision branches unlabelled. A diamond with two unlabelled arrows is genuinely ambiguous: readers cannot tell which path is "yes". Always write the condition on each branch. Third, avoid inventing custom shapes with private meanings; if you must, include a legend, but prefer standard symbols so your diagram is portable. Atlas Diagram Studio ships a full library of standard flowchart shapes at /diagram-tools/flowchart-maker, so you can grab the correct symbol rather than approximating it, and its templates keep sizing and styling consistent across a diagram.