Gerber File Extensions from Different Software: A Complete PCB Engineer’s Guide

If you’ve ever exported Gerber files from your PCB design software and wondered why the file extensions look completely different from your colleague’s files, you’re not alone. Understanding Gerber file extensions from different software is one of those practical skills that separates experienced PCB engineers from beginners. After years of working with various CAD tools and dealing with fabrication houses, I’ve learned that knowing these extensions inside-out can save you countless hours of troubleshooting and prevent costly manufacturing delays.

What Are Gerber Files and Why Do Extensions Matter?

Gerber files serve as the universal language between PCB designers and manufacturers. They’re essentially 2D vector images that describe every layer of your printed circuit board, from copper traces to solder masks to silkscreen markings. The format was originally developed by Gerber Scientific in the 1960s and has since become the de facto industry standard.

Here’s where things get interesting: while the Gerber format itself is standardized, the file extensions that different CAD software packages use are anything but standardized. Each software vendor has developed their own naming conventions, which means the same layer (let’s say, your top copper layer) could be named .GTL in Altium, .TOP in PADS, or F.Cu.gbr in KiCad.

This matters because when you send your files to a PCB manufacturer, their CAM engineers need to identify each layer correctly. Misidentified layers can lead to reversed boards, incorrect solder masks, or even completely unusable PCBs. Trust me, I’ve seen it happen, and it’s never a fun conversation with your project manager.

Understanding Gerber Format Versions

Before diving into specific software extensions, let’s quickly cover the Gerber format versions you’ll encounter.

RS-274-D (Standard Gerber)

This is the original format, and frankly, you should avoid it whenever possible. RS-274-D requires a separate aperture file to define the shapes used in your design, which creates additional complexity and potential for errors. Most modern manufacturers won’t even accept RS-274-D files anymore.

RS-274-X (Extended Gerber)

This format, also known as Gerber X1, embeds aperture definitions directly within the file. It’s self-contained, widely supported, and should be your go-to format for most fabrication jobs. When someone mentions “Gerber files” without specifying a version, they usually mean RS-274-X.

Gerber X2 and X3

Released in 2014 and 2020 respectively, these newer formats add metadata attributes that help manufacturers automatically identify layer functions, component information, and other details. Gerber X2 is backward compatible with RS-274-X, so there’s no downside to using it if your software supports it.

Gerber File Extensions from Major PCB Design Software

Now let’s get into the meat of this guide. Below is a comprehensive breakdown of Gerber file extensions generated by the most popular PCB design software packages.

Altium Designer / Protel Extensions

Altium Designer (and its predecessor Protel) uses what’s often called the “Protel naming convention,” which has become something of an informal industry standard. Many manufacturers prefer receiving files with these extensions because they’re instantly recognizable.

Layer Type	Extension	Description
Top Copper	.GTL	Gerber Top Layer
Bottom Copper	.GBL	Gerber Bottom Layer
Inner Layer 1	.G1	First inner copper layer
Inner Layer 2	.G2	Second inner copper layer
Top Solder Mask	.GTS	Gerber Top Solder mask
Bottom Solder Mask	.GBS	Gerber Bottom Solder mask
Top Silkscreen	.GTO	Gerber Top Overlay
Bottom Silkscreen	.GBO	Gerber Bottom Overlay
Top Paste	.GTP	Gerber Top Paste mask
Bottom Paste	.GBP	Gerber Bottom Paste mask
Board Outline	.GKO / .GM1	Keep-out or Mechanical layer
Drill File	.TXT / .DRL	Excellon NC drill data

The logic behind Altium’s naming is actually quite intuitive once you understand it: “G” for Gerber, “T” or “B” for Top or Bottom, and then a letter indicating the layer type (L for Layer/copper, S for Solder mask, O for Overlay/silkscreen, P for Paste).

KiCad Extensions

KiCad, being open-source, takes a more descriptive approach to file naming. This can be helpful for beginners but sometimes causes confusion with automated systems at fabrication houses.

Layer Type	Extension	Description
Top Copper	-F_Cu.gbr	Front Copper
Bottom Copper	-B_Cu.gbr	Back Copper
Inner Layer 1	-In1_Cu.gbr	Inner Layer 1 Copper
Inner Layer 2	-In2_Cu.gbr	Inner Layer 2 Copper
Top Solder Mask	-F_Mask.gbr	Front Mask
Bottom Solder Mask	-B_Mask.gbr	Back Mask
Top Silkscreen	-F_SilkS.gbr	Front Silkscreen
Bottom Silkscreen	-B_SilkS.gbr	Back Silkscreen
Top Paste	-F_Paste.gbr	Front Paste
Bottom Paste	-B_Paste.gbr	Back Paste
Board Outline	-Edge_Cuts.gbr	Edge Cuts layer
Drill File	.drl	Excellon drill file

KiCad also offers an option to use “Protel filenames,” which generates extensions compatible with the Altium convention. I generally recommend enabling this option when submitting files to manufacturers, as it reduces the chance of layer identification errors.

Autodesk EAGLE Extensions

EAGLE uses a slightly different convention that reflects its origin as a simpler, more accessible PCB tool.

Layer Type	Extension	Description
Top Copper	.CMP / .TOP	Component side copper
Bottom Copper	.SOL / .BOT	Solder side copper
Inner Layer 2	.LY2	Layer 2
Inner Layer 3	.LY3	Layer 3
Top Solder Mask	.STC / .TSM	Top Solder mask
Bottom Solder Mask	.STS / .BSM	Bottom Solder mask
Top Silkscreen	.PLC / .TSK	Top Silkscreen
Bottom Silkscreen	.PLS / .BSK	Bottom Silkscreen
Top Paste	.CRC / .TSP	Top Paste
Bottom Paste	.CRS / .BSP	Bottom Paste
Board Outline	.DIM / .MIL / .GML	Dimension/Milling layer
Drill File	.DRD / .XLN	Drill data

EAGLE’s CAM processor is quite flexible, allowing you to customize output extensions. If you’re working with EAGLE, I’d suggest setting up a CAM job that outputs Protel-compatible extensions for easier manufacturer communication.

Cadence OrCAD Extensions

OrCAD tends to use a more verbose naming approach with .art or .PHO extensions.

Layer Type	Extension	Description
Top Copper	TOP.art / L1.PHO	Top signal layer
Bottom Copper	BOTTOM.art / L2.PHO	Bottom signal layer
Inner Layers	IN1.art / L3.PHO	Inner layer artwork
Top Solder Mask	SOLDERTOP.art / MT.PHO	Top mask
Bottom Solder Mask	SOLDERBOT.art / MB.PHO	Bottom mask
Top Silkscreen	SILKTOP.art / ST.PHO	Top silkscreen
Bottom Silkscreen	SILKBOT.art / SB.PHO	Bottom silkscreen
Top Paste	PASTETOP.art / PT.PHO	Top paste
Bottom Paste	PASTEBOT.art / PB.PHO	Bottom paste
Board Outline	OUTLINE.art	Board outline
Drill File	.TAP / .DRL	Drill file

Many fabricators request that OrCAD users rename their files to follow the Protel convention before submission, as the .art and .PHO extensions aren’t automatically recognized by some CAM systems.

Mentor PADS Extensions

PADS uses yet another naming scheme that can sometimes confuse automated layer detection systems.

Layer Type	Extension	Description
Top Copper	.TOP	Top copper
Bottom Copper	.BOT	Bottom copper
Inner Signal	.IN1, .IN2	Inner signal layers
Inner Plane	.GP1, .GP2	Internal plane layers
Top Solder Mask	.SMT	Solder mask top
Bottom Solder Mask	.SMB	Solder mask bottom
Top Silkscreen	.SST	Silkscreen top
Bottom Silkscreen	.SSB	Silkscreen bottom
Top Paste	.SPT	Solder paste top
Bottom Paste	.SPB	Solder paste bottom
Board Outline	.FAB	Fabrication outline
Drill File	.DRL	Drill data

Best Practices for Managing Gerber File Extensions

After dealing with hundreds of PCB designs, here are my recommendations for avoiding extension-related headaches:

Always Include a README File

Include a simple text file in your Gerber package that maps each file to its layer function. This takes five minutes and can save days of back-and-forth with your manufacturer.

Verify Before You Submit

Use a Gerber viewer to load all your files and visually confirm that each layer displays correctly. This simple step catches most extension-related issues before they become problems.

Stick to One Convention When Possible

If your organization uses multiple CAD tools, consider standardizing on the Protel naming convention for all Gerber exports. Most software packages support this as an output option.

Communicate with Your Manufacturer

Different fabrication houses have different preferences. Some have automated systems that work better with certain extensions. A quick email asking about their preferred format can prevent issues down the line.

Useful Resources and Tools

Here are some valuable resources for working with Gerber files:

Free Gerber Viewers

Software	Platform	Download Link
Gerbv	Windows, Linux	https://gerbv.github.io/
ViewMate	Windows	https://www.pentalogix.com/t/software-products/viewmate
ZofzPCB	Windows	https://www.zofzpcb.com/
HQDFM Online	Web-based	https://www.nextpcb.com/free-online-gerber-viewer.html
GerberLogix	Windows	https://www.easylogix.de/

Gerber Format Documentation

The official Gerber format specification is maintained by Ucamco and is freely available. You can download the complete specification at https://www.ucamco.com/gerber to understand exactly what’s inside these files.

Common Gerber Extension Mistakes to Avoid

Through my experience, these are the most common extension-related errors I’ve encountered:

Mixing Conventions

Don’t mix naming conventions in the same project. If you start with Protel extensions, stick with them throughout. Mixed naming confuses both automated systems and human reviewers.

Forgetting the Drill File

The drill file (usually .TXT, .DRL, or .XLN) isn’t technically a Gerber file, but it’s essential for manufacturing. Make sure it’s included and uses compatible coordinate settings with your Gerber files.

Incorrect Board Outline Extension

The board outline is critical for defining your PCB’s physical shape. Different software uses different default extensions (.GKO, .GM1, .Edge_Cuts), and missing or misnamed outline files are a common cause of fabrication delays.

Frequently Asked Questions

What is the standard Gerber file extension?

The official standard extension for Gerber files is .GBR or .gbr. However, in practice, most PCB design software uses layer-specific extensions like .GTL (top copper), .GBL (bottom copper), .GTS (top solder mask), etc., which are based on the Protel/Altium naming convention. These descriptive extensions help manufacturers quickly identify each layer’s function without needing to open the files.

Can I rename Gerber files to different extensions?

Yes, you can safely rename Gerber files because the file extension doesn’t change the actual data inside the file. However, be careful to maintain a clear mapping of which file corresponds to which layer. Always include documentation when submitting renamed files to your manufacturer, and verify the renamed files still open correctly in a Gerber viewer before submission.

Why do different PCB software use different Gerber extensions?

Each PCB design software developer created their own naming conventions before any industry-wide standard was established. While the Gerber format itself is standardized, the file naming conventions evolved independently within each software ecosystem. The Protel convention has become the most widely recognized, which is why many other software packages now offer it as an export option.

How do I know if my Gerber files are RS-274X or RS-274D format?

Open any of your Gerber files in a text editor. RS-274X files contain embedded aperture definitions that start with %ADD commands near the beginning of the file. RS-274D files lack these definitions and require a separate aperture file. Additionally, RS-274X files typically include extended commands starting with % symbols throughout the file, while RS-274D files contain only basic coordinate and draw commands.

Which Gerber file extension should I use for the board outline?

For the board outline, the most commonly accepted extensions are .GKO (Gerber Keep-Out, from Altium/Protel), .GM1 (Gerber Mechanical 1), or software-specific names like -Edge_Cuts.gbr (KiCad) and .DIM or .GML (EAGLE). The key is ensuring your manufacturer knows which file contains the board outline. When in doubt, use .GKO as it’s the most universally recognized extension for board outlines.

Conclusion

Understanding Gerber file extensions from different software might seem like a minor detail in PCB design, but it’s one of those foundational skills that makes the entire manufacturing process smoother. Whether you’re using Altium, KiCad, EAGLE, OrCAD, or PADS, knowing how each tool names its output files helps you communicate more effectively with manufacturers and catch potential issues before they become expensive problems.

The PCB industry has evolved significantly, and while we’re still dealing with multiple naming conventions, the trend is moving toward more standardized approaches like Gerber X2 with its embedded metadata. Until full standardization arrives, keep this guide handy, always verify your files in a viewer before submission, and maintain clear documentation of your layer mappings. Your future self (and your manufacturer’s CAM engineers) will thank you.