Standard Flowchart Symbols and Their Iso Codes: a Complete Reference Guide

If you've ever opened a flowchart tool and stared at a row of shapes wondering which one means what, you're not alone. Flowchart symbols look simple, but using the wrong shape can confuse your audience, slow down a project, or make a process harder to follow. The good news is there's an actual standard behind these shapes set by ISO and once you learn it, your diagrams become clear to anyone, anywhere in the world.

What are standard flowchart symbols?

Standard flowchart symbols are the agreed-upon shapes used in process diagrams to represent specific actions, decisions, inputs, outputs, and flow directions. These symbols were formalized so that engineers, developers, business analysts, and project managers could all read the same diagram without miscommunication.

The most widely referenced standard is ISO 5807:1985, titled "Information processing Documentation symbols and conventions for data, program and system flowcharts, program network charts and system resources charts." This standard defines which shapes map to which functions. If you're just starting out, our beginner's breakdown of flowchart symbol codes covers the basics in more detail.

Why do ISO codes matter for flowchart symbols?

Without a shared standard, every team could use shapes differently. A diamond might mean "decision" in one company and "data input" in another. ISO 5807 removes that guesswork. Here's why it matters:

Cross-team clarity Developers, designers, and stakeholders all read the diagram the same way.
Audit and compliance Industries like healthcare, manufacturing, and finance often require standardized documentation.
Tool compatibility Most flowchart software (Lucidchart, Microsoft Visio, draw.io) uses ISO-aligned symbol libraries by default.
Long-term usability A diagram made today stays readable years later, even if the team changes.

What does each standard flowchart symbol mean?

Here are the core symbols defined in ISO 5807, along with their common names and what they represent:

Terminal (Start/End)

Shape: Rounded rectangle or oval.
ISO reference: Symbol 1 in ISO 5807.
Use: Marks where a process begins or ends. Every flowchart should have at least one start and one end terminal.

Process

Shape: Rectangle.
ISO reference: Symbol 2.
Use: Represents an action, operation, or step in the process like "Submit form" or "Calculate total."

Decision

Shape: Diamond.
ISO reference: Symbol 4.
Use: A point where the flow branches based on a yes/no or true/false condition. Example: "Is the order above $100?"

Input/Output (Data)

Shape: Parallelogram.
ISO reference: Symbol 3.
Use: Represents data entering or leaving the process like reading user input or writing to a database.

Flow Lines (Arrows)

Shape: Arrows or lines connecting shapes.
ISO reference: Symbol 5.
Use: Shows the direction of the process flow. Arrows connect symbols in the order steps occur.

Connector

Shape: Small circle.
ISO reference: Symbol 7.
Use: Links different parts of a flowchart, especially when the diagram spans multiple pages or sections.

Predefined Process

Shape: Rectangle with double vertical lines on each side.
ISO reference: Symbol 8.
Use: Refers to a process that's defined elsewhere like a subroutine or a separate documented procedure.

Document

Shape: Rectangle with a wavy bottom edge.
ISO reference: Symbol 12.
Use: Indicates a document or report is generated or referenced at that step.

Manual Operation

Shape: Trapezoid.
ISO reference: Symbol 14.
Use: A step that must be performed manually by a person, not automated.

Annotation (Comment)

Shape: Rectangle with a vertical line on the left side.
ISO reference: Symbol 10.
Use: Adds explanatory notes or comments to a specific step in the diagram.

For software-specific workflows, some of these symbols get used in unique ways. We cover those scenarios in our article on flowchart symbol codes for software development workflows.

How do ISO flowchart symbols compare across different standards?

While ISO 5807 is the most cited international standard, you may also encounter symbols from:

ANSI X3.5 The American National Standards Institute version. Largely overlaps with ISO 5807 but has minor shape variations.
IEC 60617 Focused on electrical and electronic diagrams. Shares some logic symbols with flowcharts but serves a different domain.
BPMN (Business Process Model and Notation) A more modern notation for business workflows. Not a replacement for ISO 5807, but an alternative for business process mapping.

In most everyday use, ISO 5807 and ANSI X3.5 are nearly interchangeable. If your team works internationally, sticking with ISO 5807 keeps things consistent.

When should you use ISO-standard flowchart symbols?

You don't always need strict ISO compliance. Here's a practical breakdown:

Use ISO-standard symbols when documenting processes for audits, regulatory submissions, cross-functional teams, or external stakeholders.
Use simplified symbols for quick whiteboard sketches, internal brainstorming, or informal team discussions.

The key is matching the formality of your symbols to the formality of the audience. A napkin sketch doesn't need ISO accuracy. A process document going to a compliance team does.

What are common mistakes people make with flowchart symbols?

Using rectangles for everything. This makes decision points invisible and defeats the purpose of a flowchart.
Mixing up diamonds and parallelograms. A diamond means a yes/no decision. A parallelogram means data in or data out. Swapping them confuses readers.
Missing start/end terminals. Without these, readers don't know where the process begins or ends.
Arrow direction inconsistency. Flow should generally move top-to-bottom or left-to-right. Mixing directions creates visual confusion.
Overcomplicating the diagram. If your flowchart has 50+ symbols, consider breaking it into subprocesses using predefined process symbols.

Tips for creating clear, standard-compliant flowcharts

Start with the process steps in plain text before drawing anything. Map out what happens first, second, and third.
Use one symbol per type of action. Don't reuse a process rectangle for a decision point just because it fits.
Label every arrow leaving a decision diamond with "Yes" or "No" (or the relevant condition).
Keep your flowchart on one page if possible. Use connectors to link sections if it gets too long.
Use consistent spacing and alignment. Messy layouts make even correct symbols hard to read.
Test your flowchart by giving it to someone unfamiliar with the process and asking them to explain it back to you.

If you want a deeper reference on all the symbol codes in one place, our complete guide to standard flowchart symbols and their ISO codes lists every recognized symbol with visual examples.

Quick reference checklist before you publish a flowchart

Every process has a clear start terminal and at least one end terminal.
Decision diamonds have labeled branches (Yes/No, True/False, or specific conditions).
Data inputs and outputs use parallelograms, not rectangles.
Arrows show a consistent flow direction (top-to-bottom or left-to-right).
Predefined processes are used for subprocesses defined elsewhere.
The diagram follows ISO 5807 or ANSI X3.5 conventions if it's for external or compliance use.
Someone unfamiliar with the process can follow the flowchart without additional explanation.

Start by auditing one of your existing flowcharts against this checklist. You'll likely find two or three symbols that are slightly off and fixing them takes less than five minutes but makes the diagram significantly easier to read.

Reference: ISO 5807:1985 Information processing Documentation symbols and conventions