Flowchart symbols and what each one means

Flowchart symbols are a small shared vocabulary. Used properly, a reader knows what a shape means before they read the words inside it. Used loosely, the shapes stop carrying information and you may as well have drawn everything as rectangles.

Here is the set that actually gets used, and what each shape is for.

The five you will use constantly

Terminator — the stadium shape. The start or the end. Every flowchart has exactly one start, and at least one end. If a chart has no terminator, a reader cannot tell where to begin.

Process — the rectangle. A single action. The test of a good process box is that you cannot put the word “and” in it. “Check the stock and pack the box” is two steps pretending to be one, and splitting them usually reveals that different people do them.

Decision — the diamond. A question with a small number of answers. Every line leaving a diamond must be labelled with the answer it represents. An unlabelled branch is the single most common flowchart error and it makes the chart unusable.

Data — the parallelogram. Something entering or leaving the process: a form submitted, a file received, a report produced. It answers “where did that come from” without a paragraph of explanation.

Arrow — the connector. Direction of flow. Arrows always point the way the process moves. Lines without arrowheads leave the reader guessing.

The ones worth knowing

Predefined process — the rectangle with two side bars. A step that is defined properly somewhere else. Use it to keep one chart to one page instead of inlining a whole sub-procedure.

Document — the rectangle with a wavy bottom. A step that produces something a person reads: an invoice, a letter, a report.

Database — the cylinder. Data at rest. Reading from or writing to stored records.

Manual input — the shape with a sloped top. Someone types something in. Useful when you want to make the human effort in a process visible.

Delay — the D shape. Waiting. Putting delays in explicitly is often the most valuable thing a process map does, because waiting is usually where the time actually goes.

Off-page connector — the home-plate pentagon. The flow continues on another page or another diagram. Give it a label and use the same label at the other end.

On-page connector — the small circle. Joins two parts of the same diagram without dragging a line across the whole page. Number them in pairs.

Three mistakes that spoil a flowchart

Unlabelled decision branches. If a diamond has two lines out and neither says Yes or No, the diagram has lost the information it was drawn to carry. Label every branch, always.

Diamonds used as junctions. A diamond means a decision is being made. If you just need several arrows to meet, use a small circle or let the lines converge on the next box.

A process box that is really a decision. “Check whether the order is complete” is not an action, it is a question, and it should be a diamond with labelled exits. This one is subtle and very common.

Does the shape really matter?

For a sketch you will throw away, no. For anything somebody else will read, yes, and for two reasons.

The first is speed. A reader who knows the vocabulary takes in the structure of a page-long chart in a couple of seconds, purely from the outlines, before reading a single word.

The second is that choosing the shape forces you to decide what a step actually is. Working out whether something is a process or a decision is frequently the moment you realise that the step you wrote down is two steps, or that nobody owns it.

If you are drawing for an exam or a certification, the shapes are usually marked, and the set above is what is expected. The sheet below puts them on one printable page, and the programming flowcharts show them at work in nine worked exercises.