Industrial automation has transformed modern manufacturing, and at the heart of this transformation lies the PLC (Programmable Logic Controller). Whether you’re controlling conveyor belts, robotic arms, packaging systems, or complex manufacturing processes, PLCs make automation reliable, accurate, and efficient. However, a PLC is only as effective as the code that powers it. That’s where PLC programming languages become essential.
Think of PLC programming languages as the voice you use to talk to a machine. Without the right language, the machine simply won’t understand what you want it to do. Every automated system you see in a factory floor — every motor that starts on time, every valve that opens at exactly the right moment — is running on logic written in one of these languages.
To bring some order to all of this, the IEC 61131-3 standard was introduced as a global benchmark. It defines the five official PLC programming languages that engineers use worldwide today.
In this guide, we’ll walk through all the types of PLC programming languages, what makes each one unique, how they compare, and how to figure out which one actually fits your needs.
What Are PLC Programming Languages?
A PLC (Programmable Logic Controller) is basically a ruggedized industrial computer built to control machines and processes in real time. Unlike your laptop, it doesn’t crash when things get dusty or hot — it’s designed to run 24/7 in tough factory environments without breaking a sweat.
Now, what are the PLC programming languages exactly? Simply put, they’re the set of languages engineers use to write the logic that tells a PLC what to do. When should a motor start? When should it stop? What happens if a sensor detects something unusual? All of that decision-making is written in a PLC programming language.
Before these languages were standardized, every PLC manufacturer had their own way of doing things. It was messy. So in 1993, the IEC 61131-3 standard came along and changed everything — it defined five official languages that work across different PLC platforms.
Choosing the right language isn’t just a technical decision. It affects how easy your code is to read, debug, and maintain down the line. And in industrial automation, that matters more than most people realize.
Types of PLC Programming Languages
So how many PLC programming languages are there? According to the IEC 61131-3 standard, there are officially five types of PLC programming languages — and each one was designed with a different kind of engineer in mind.
Here’s a quick look at all five before we dig deeper into each one:
1. Ladder Diagram (LD)
This is the most popular one by far. It looks like an electrical relay circuit drawn on a ladder — which is exactly why electricians love it. If you’ve ever worked with relay logic, you’ll feel right at home here.
2. Function Block Diagram (FBD)
This one is more visual and flow-based. You connect blocks together like a signal chain, which makes it great for process control applications. Engineers who think in terms of inputs and outputs tend to prefer this language.
3. Structured Text (ST)
Think of this as the “programming language” of the group. It looks a lot like Pascal or C, and it’s perfect for writing complex logic, math operations, and algorithms. Software developers switching to PLC work usually gravitate toward this one.
4. Instruction List (IL)
This is the oldest of the different types of PLC programming languages — low-level, assembly-like, and honestly a bit old-fashioned now. It’s mostly found in legacy systems these days.
5. Sequential Function Chart (SFC)
This one works like a flowchart. It’s ideal for processes that happen in a clear step-by-step sequence, like batch manufacturing or bottling lines.
| Also Read: If you’re curious about newer and emerging programming languages beyond PLCs, check out our detailed guide on the Verse Programming Language right here on Cybersolvings. |
Common PLC Programming Languages Explained
Let’s get into the real detail now. Here’s a proper breakdown of all the common PLC programming languages you’ll encounter in the field — what they look like, how they work, and where they actually shine.
1. Ladder Diagram (LD)
If there’s one language that dominates the automation world, it’s Ladder Diagram. It’s easily the most widely used of all PLC programming languages, and for good reason.
The language gets its name from how it looks — a series of rungs on a ladder, each rung representing a piece of logic. It was designed to mimic old-school relay circuits, so electricians and control engineers who came from an electrical background could pick it up without having to learn “programming” in the traditional sense.
Each rung contains contacts (inputs) and coils (outputs). If the input conditions are met, the output activates. Simple as that.
Best for: Discrete control, simple ON/OFF logic, motor starters, conveyor systems.
Real-world example: Imagine a conveyor belt that should only run when a safety door is closed and a start button is pressed. That kind of straightforward logic is exactly what Ladder Diagram was built for. It’s clear, it’s visual, and almost any maintenance technician can read it without much training.
2. Function Block Diagram (FBD)
Function Block Diagram takes a more graphical, signal-flow approach. Instead of rungs, you work with blocks — each block represents a function — and you connect them together using lines that show how signals flow from one block to the next.
It’s a bit like drawing a wiring diagram for your logic rather than writing it out.
Best for: Analog control, PID loops, process industries like water treatment, oil and gas, and chemical plants.
Engineers who work in process control tend to love FBD because it maps closely to how they already think about systems — in terms of inputs feeding into processes and producing outputs. It’s also easier to visualize feedback loops and control structures compared to Ladder Diagram.
3. Structured Text (ST)
This is where things get interesting for anyone with a software development background. Structured Text is a high-level, text-based language that looks a lot like Pascal or even a simplified version of C.
You write actual code — with variables, loops, conditionals, and functions. It’s the most powerful of all the PLC programming languages when it comes to handling complex math, data manipulation, and advanced algorithms.
Best for: Data processing, advanced motion control, complex calculations, and anywhere you need logic that goes beyond simple ON/OFF decisions.
If you need to calculate a moving average, run a custom control algorithm, or handle large data arrays, Structured Text is your go-to. The learning curve is steeper than Ladder Diagram, but the flexibility it gives you is worth it.
4. Instruction List (IL)
Instruction List is the oldest language in the group. It’s low-level and assembly-like — you write out commands one line at a time, almost like giving a machine direct instructions at the hardware level.
Honestly? It’s not used much anymore. The IEC 61131-3 standard actually deprecated it in its 2013 revision, which tells you a lot about where the industry stands on it.
Best for: Legacy systems that were programmed decades ago, or situations where you need very fine-tuned, optimized performance at a low level.
If you encounter IL in the field, it’ll almost always be in older equipment. Don’t bother learning it from scratch — focus your energy on the other languages instead.
5. Sequential Function Chart (SFC)
Sequential Function Chart works like a flowchart. You define steps, transitions between those steps, and the conditions that trigger each transition. It’s visual, structured, and makes complex sequences surprisingly easy to follow.
Best for: Batch processes, automated assembly lines, bottling plants, and any application where things need to happen in a specific, repeatable order.
Real-world example: Picture a bottling line — fill the bottle, cap it, label it, pack it. Each stage is a step, and SFC maps out exactly when and how the system moves from one stage to the next. Trying to write that same logic in a Ladder Diagram would get messy fast. In SFC, it’s clean and easy to follow.
PLC Programming Languages List at a Glance
At this point, you’ve got a solid understanding of each language individually. But sometimes it helps to see everything side by side. Here’s a clean PLC programming languages list that gives you the full picture at a glance — so you can quickly compare and reference without having to scroll back through everything.
| Language | Type | Best For | Skill Level | Still Active? |
| Ladder Diagram (LD) | Graphical | Discrete control, ON/OFF logic | Beginner | ✅ Yes |
| Function Block Diagram (FBD) | Graphical | Process control, PID loops | Intermediate | ✅ Yes |
| Structured Text (ST) | Text-based | Complex logic, math, algorithms | Advanced | ✅ Yes |
| Instruction List (IL) | Text-based | Legacy systems only | Advanced | ⚠️ Deprecated |
| Sequential Function Chart (SFC) | Graphical | Batch processes, sequential steps | Intermediate | ✅ Yes |
PLC Programming Languages Comparison
Knowing what each language does is one thing — but understanding how they stack up against each other is what actually helps you make smart decisions on the job. Here’s a detailed PLC programming languages comparison across the factors that matter most in real automation work.
| Factor | Ladder Diagram (LD) | Function Block Diagram (FBD) | Structured Text (ST) | Instruction List (IL) | Sequential Function Chart (SFC) |
| Readability | ⭐⭐⭐⭐⭐ Very easy | ⭐⭐⭐⭐ Easy | ⭐⭐⭐ Moderate | ⭐⭐ Difficult | ⭐⭐⭐⭐ Easy |
| Writing Speed | ⭐⭐⭐⭐ Fast | ⭐⭐⭐⭐ Fast | ⭐⭐⭐ Moderate | ⭐⭐ Slow | ⭐⭐⭐ Moderate |
| Handling Complex Logic | ⭐⭐ Limited | ⭐⭐⭐ Good | ⭐⭐⭐⭐⭐ Excellent | ⭐⭐⭐ Good | ⭐⭐⭐ Good |
| Learning Curve | ✅ Easiest | 🟡 Moderate | 🔴 Steepest | 🔴 Steep | 🟡 Moderate |
| Industry Adoption | 🏆 Highest | ⭐ High | ⭐ Growing fast | ❌ Declining | ⭐ Moderate |
| Best User Background | Electricians | Process Engineers | Software Developers | Legacy Specialists | Automation Engineers |
| Debugging Ease | ⭐⭐⭐⭐⭐ Very easy | ⭐⭐⭐⭐ Easy | ⭐⭐⭐ Moderate | ⭐⭐ Difficult | ⭐⭐⭐⭐ Easy |
| Reusability of Code | ⭐⭐ Low | ⭐⭐⭐⭐ High | ⭐⭐⭐⭐⭐ Very High | ⭐⭐ Low | ⭐⭐⭐ Moderate |
| Suitable for Large Projects | 🟡 Partially | ✅ Yes | ✅ Yes | ❌ No | ✅ Yes |
| IEC 61131-3 Status | ✅ Active | ✅ Active | ✅ Active | ⚠️ Deprecated | ✅ Active |
How to Choose the Right PLC Programming Language
Honestly, there’s no universal “best” PLC programming language. The right choice depends on your situation — and a few key factors can point you in the right direction pretty quickly.
Your background matters a lot. If you came up through electrical work, Ladder Diagram is going to feel natural almost immediately. If you’re a software developer jumping into automation, Structured Text will make way more sense to you. Don’t fight your background — lean into it.
Think about what you’re actually building. Simple ON/OFF discrete control? Ladder Diagram handles that easily. Working on a process plant with PID loops and analog signals? FBD is your friend. Building a sequential batch process? SFC was literally made for that. Motion control with heavy math? That’s Structured Text territory.
Your PLC brand plays a role too. Siemens TIA Portal supports all five languages, but ST and LAD are most common there. Allen-Bradley’s Studio 5000 heavily favors Ladder. Mitsubishi and Omron have their own preferences as well. Always check what your platform supports well before committing to a language.
Don’t overlook your team. You might personally love Structured Text, but if the rest of your team only knows Ladder Diagram, writing everything in ST creates a maintenance nightmare down the road. The best code is code that everyone on your team can actually read and fix at 2am when something breaks.
Industry Applications of Different PLC Programming Languages
Different industries have naturally gravitated toward different PLC programming languages over the years — mostly based on what works best for their specific processes. Here’s how it typically breaks down in the real world.
Manufacturing is where the Ladder Diagram has always been king. Most factory floors are full of discrete operations — conveyors, presses, assembly stations — and LD handles all of that cleanly. It’s also easy for maintenance technicians to troubleshoot on the spot, which matters a lot in a production environment where downtime is expensive.
Oil & Gas and Chemical plants tend to lean on FBD and SFC. These industries deal with continuous processes, complex control loops, and sequences that need to be executed in a very precise order. FBD handles the control logic beautifully, while SFC manages the step-by-step process flow without things getting messy.
Robotics and Motion Control is where Structured Text really shines. The math involved — trajectory calculations, speed profiling, position control — is just too complex for graphical languages to handle comfortably. ST gives engineers the flexibility to write that logic properly.
Food and Beverage heavily relies on SFC for batch sequencing. Mix this ingredient, heat to this temperature, hold for this long, then move to the next stage — that’s textbook SFC territory.
Building Automation usually mixes FBD and Ladder Diagram depending on the system. HVAC control loops suit FBD, while simpler on/off lighting or access control systems stick with LD.
Conclusion
At the end of the day, there’s no single “best” language in the world of PLC programming languages — each one exists for a reason, and each one does its job well in the right context. Ladder Diagram keeps factory floors running. Structured Text handles the complex stuff. FBD and SFC bring clarity to process and sequential control. Even the Instruction List had its moment.
If you’re just starting out, begin with Ladder Diagram — it’s beginner-friendly, widely used, and will get you productive fast. Once you’re comfortable, start exploring the others. The more languages you know, the more valuable you become as an automation engineer.
Want to keep learning about automation, programming, and industrial technology? Explore more in-depth guides right here on Cybersolvings — there’s a lot more where this came from.
Frequently Asked Questions (FAQs)
Q1. What are the PLC programming languages defined by IEC 61131-3?
IEC 61131-3 defines five PLC programming languages — Ladder Diagram, Function Block Diagram, Structured Text, Instruction List, and Sequential Function Chart. Each serves a different purpose in industrial automation.
Q2. Which PLC programming language should a beginner learn first?
Ladder Diagram is the best starting point for beginners. It’s visual, easy to understand, and the most widely used PLC programming language across real-world industrial automation projects.
Q3. What is the difference between Ladder Diagram and Structured Text?
Ladder Diagram is graphical and ideal for simple discrete logic, while Structured Text is code-based and better suited for complex algorithms, math operations, and advanced automation applications.
