How to Convert Gerber RS-274D to RS-274X (Extended Gerber): Complete Guide

If you’ve been in the PCB industry long enough, you’ve probably encountered those frustrating legacy Gerber files that seem impossible to process. Maybe you inherited an old design, received files from a customer with outdated CAD software, or pulled archived data from a decade-old project. The culprit is often RS-274D, the original “Standard Gerber” format that was officially revoked in 2014 but still haunts our industry. This guide explains how to convert Gerber RS-274D to RS-274X (Extended Gerber), why this conversion matters, and what tools can help you get the job done right.

Understanding the Difference Between RS-274D and RS-274X

Before diving into the conversion process, it’s important to understand what makes these formats different. This isn’t just academic knowledge. Grasping the fundamental distinction will help you troubleshoot problems when conversions don’t go smoothly.

What is RS-274D (Standard Gerber)?

RS-274D was developed by Gerber Systems Corp in the 1960s and 1970s to drive vector photoplotters. It’s a simple ASCII format containing commands and X-Y coordinates, but here’s the critical problem: RS-274D is not self-contained. The format doesn’t include aperture definitions, coordinate units, or other essential information needed to interpret the file correctly.

RS-274D Characteristic	Description
Aperture Information	External file required (wheel file/aperture table)
Coordinate Units	Not specified in file
Zero Suppression	Not standardized
Coordinate Format	Not embedded
File Extension	Various (.gbr, .ger, .pho, .art)
Status	Revoked by Ucamco in 2014

The aperture definitions were historically stored in a separate “wheel file” or “aperture table.” This approach made sense when a physical aperture wheel needed to be mounted on the photoplotter, but it creates serious problems for modern digital workflows.

What is RS-274X (Extended Gerber)?

RS-274X, released in 1998 by Ucamco (formerly Barco ETS), solved the fundamental problem of RS-274D by embedding all critical information within the Gerber file itself. This makes RS-274X files self-describing and eliminates the need for separate aperture files.

RS-274X Characteristic	Description
Aperture Information	Embedded in file header
Coordinate Units	Explicitly defined (MO parameter)
Zero Suppression	Specified in format statement
Coordinate Format	Defined by FS parameter
Standard Apertures	Circle (C), Rectangle (R), Obround (O), Polygon (P)
Custom Apertures	Aperture macros supported
Polarity Control	Dark/Clear polarity supported
Status	Current industry standard

Why Convert RS-274D to RS-274X?

The reasons to convert are compelling:

Problem with RS-274D	Solution in RS-274X
Missing aperture file causes “undefined D-code” errors	Apertures embedded, no external files needed
Coordinate misinterpretation (wrong scale)	Units and format explicitly defined
Manual workflow required	Automated processing possible
Error-prone data transfer	Self-contained, reliable transfer
Limited manufacturer acceptance	Universally accepted
No support for complex shapes	Aperture macros for any shape

Identifying RS-274D vs RS-274X Files

Before you can convert, you need to confirm what you’re dealing with. Open the Gerber file in a text editor (Notepad, Notepad++, or any plain text editor) and examine the content.

Signs of an RS-274D File

An RS-274D file typically starts directly with coordinates and D-codes without any header parameters:

D11*X1785250Y2173980D02*X1796650Y2177730D01*X1785250Y2181480D01*D12*X3421095Y1407208D03*M02*

Notice there are no aperture definitions. The file assumes you have a separate aperture table that defines what D11 and D12 actually look like.

Signs of an RS-274X File

An RS-274X file contains embedded parameters at the beginning:

G04 Gerber RS-274X Example*%FSLAX36Y36*%%MOMM*%%ADD10C,0.150*%%ADD11R,1.600X0.800*%%ADD12O,2.000X1.000*%D10*X25400000Y12700000D02*X50800000Y12700000D01*M02*

The key indicators are:

• %FS…% – Format Statement defining coordinate interpretation
• %MO…% – Mode (MM for millimeters, IN for inches)
• %AD…% – Aperture Definitions embedded in the file

Step-by-Step Guide to Convert RS-274D to RS-274X

The conversion process requires combining the RS-274D coordinate data with aperture information to create a self-contained RS-274X file. Here’s how to do it:

Step 1: Gather All Required Files

For a successful conversion, you need:

Required Item	Purpose
RS-274D Gerber files	The actual layer data
Aperture table/wheel file	Defines D-code shapes and sizes
Format information	Units, coordinate format, zero suppression

The aperture file might have extensions like .apt, .rep, .whl, or be embedded in a README or documentation file. If you don’t have an aperture file, you’ll need to recreate it manually, which is challenging but not impossible.

Step 2: Determine the Coordinate Format

Before loading files into a conversion tool, you must know:

Parameter	Common Values	How to Determine
Units	Inches or Millimeters	Check documentation or measure known features
Integer digits	2-4	Usually 2 for inches, 3-4 for mm
Decimal digits	3-6	Determines precision
Zero suppression	Leading, Trailing, or None	Check documentation
Coordinates	Absolute or Incremental	Usually absolute

A common format is 2.4 (two integer, four decimal digits) for inch units, or 3.3 or 4.4 for millimeter units. If the format is wrong, your design will appear at the wrong scale (often 10x too large or too small).

Step 3: Load Files into Conversion Software

Using a capable Gerber viewer/converter like GerbView, follow these steps:

Configure Format Settings First

Before loading files, set the expected format parameters in the software:

1. Open application settings or preferences
2. Navigate to Gerber format settings
3. Set units (inches or millimeters)
4. Set coordinate format (integer.decimal digits)
5. Set zero suppression mode
6. Set coordinate mode (absolute/incremental)

Load the Gerber Layers

1. Use the “Add Layer” or “Import” function
2. Select your RS-274D Gerber files
3. The software will attempt to display them

Load the Aperture Table

If the software didn’t automatically recognize apertures:

1. Use the “Load Aperture” or “Import Aperture Table” function
2. Select your aperture file
3. Most software supports common aperture file formats

Manually Define Apertures (If Necessary)

If no aperture file exists, you’ll need to define each D-code manually:

1. Open the aperture editor
2. For each D-code used in the file, define:
   1. Shape (circle, rectangle, obround, etc.)
   1. Dimensions (diameter, width, height)
3. Common D-codes: D10-D99 for standard apertures

Step 4: Verify the Display

Before converting, visually verify that everything looks correct:

Check Item	Expected Result
Overall scale	Board dimensions match specifications
Pad shapes	Correct shapes and sizes
Trace widths	Match design intent
Layer alignment	All layers register correctly
No “stringy” appearance	Apertures properly applied

A “stringy” appearance where everything looks like thin lines indicates missing or incorrect aperture definitions.

Step 5: Export as RS-274X

Once everything displays correctly:

1. Navigate to File → Export or Conversion menu
2. Select RS-274X or Extended Gerber as the output format
3. Choose an output directory
4. Set file naming options
5. Execute the conversion

Important: Use different file names or extensions than the originals to avoid overwriting your source files.

Step 6: Verify the Converted Files

After conversion, verify your new RS-274X files:

1. Open the converted files in a fresh session
2. They should load without requiring external aperture files
3. Visually compare to the original display
4. Check that embedded apertures match your definitions

Conversion Tools and Software

Several tools can perform RS-274D to RS-274X conversion:

Commercial Software

Tool	Vendor	Key Features
GerbView	Software Companions	Full conversion support, 30-day trial
CAM350	DownStream Technologies	Industry standard CAM tool
ViewMate	Pentalogix	Professional Gerber viewer/editor
GerbTool	Cadence	Included with some Cadence products
FAB 3000	Numerical Innovations	Full CAM capabilities

Free/Open Source Tools

Tool	Platform	Limitations
Gerbv	Windows/Linux	RS-274X viewer only (no RS-274D conversion)
KiCad GerbView	Cross-platform	RS-274X viewing only
Tracespace Viewer	Online	RS-274X only

Note: Most free tools only support RS-274X viewing, not RS-274D conversion. The conversion process requires commercial software in most cases.

Online Options

Several PCB manufacturers offer online Gerber viewers, but they typically don’t support RS-274D:

Service	URL	RS-274D Support
JLCPCB Viewer	jlcpcb.com	RS-274X only
PCBWay Viewer	pcbway.com	RS-274X only
GerbLook	gerblook.org	RS-274X only

Understanding Aperture Tables in Detail

Since aperture tables are the critical element that RS-274D files lack, understanding them deeply helps with conversion.

Standard Aperture Shapes

Shape Code	Name	Parameters	Example Definition
C	Circle	Diameter	%ADD10C,0.050*% (50 mil circle)
R	Rectangle	Width x Height	%ADD11R,0.060X0.080*%
O	Obround	Width x Height	%ADD12O,0.050X0.100*%
P	Polygon	OD x Vertices x Rotation	%ADD13P,0.100X6X0.0*%

D-Code Numbering Conventions

D-Code Range	Purpose
D01	Draw (pen down, light on)
D02	Move (pen up, light off)
D03	Flash (expose aperture shape)
D10-D999	User-defined apertures

When manually recreating aperture tables, you’ll need to determine what each D-code represents by examining the context in which it’s used. D-codes used with D03 (flash) commands are typically pads, while those used with D01 (draw) commands are typically traces.

Creating Aperture Files Manually

If you must recreate an aperture file from scratch:

1. List all unique D-codes in the RS-274D file
2. Examine how each D-code is used (flash vs. draw)
3. Measure corresponding features on physical boards if available
4. Use industry-standard sizes as starting points
5. Test iteratively until the display matches expectations

Common Conversion Problems and Solutions

Even with the right tools, conversion can be tricky. Here are common issues and how to resolve them:

Problem: Design Appears at Wrong Scale

Symptoms: PCB appears 10x too large or too small

Cause: Incorrect decimal digit setting

Solution: Change coordinate format. If using 2.4 and design is 10x too small, try 2.3. If 10x too large, try 2.5.

Problem: “Undefined Aperture” Errors

Symptoms: Software reports undefined D-codes

Cause: Missing aperture definitions

Solution: Load aperture file or manually define each D-code in the aperture editor.

Problem: Shapes Look Wrong

Symptoms: Rectangles appear as circles, wrong sizes

Cause: Aperture table doesn’t match file

Solution: Verify aperture table is for the correct design. Cross-reference with documentation.

Problem: Negative/Positive Polarity Issues

Symptoms: Dark areas appear clear and vice versa

Cause: Incorrect polarity setting

Solution: Toggle layer polarity in the software settings.

Problem: Coordinates Offset or Mirrored

Symptoms: Design is shifted or flipped

Cause: Origin point or mirror settings incorrect

Solution: Check offset and mirror settings in format configuration.

Best Practices for Maintaining Converted Files

Once you’ve successfully converted your RS-274D files, follow these practices:

Archive Both Versions

Keep both the original RS-274D files (with aperture tables) and the converted RS-274X files. The originals serve as a reference if questions arise.

Document the Conversion

Record:

• Date of conversion
• Software and version used
• Format settings applied
• Any manual aperture definitions
• Verification steps performed

Validate Before Manufacturing

Always verify converted files before sending to production:

1. Load in a different Gerber viewer
2. Measure known features
3. Check all layers align
4. Verify pad and trace dimensions

Working with Multiple Design Revisions

When dealing with archived projects that have multiple revisions, convert all versions to RS-274X and maintain clear version control. This prevents confusion when older revisions need to be manufactured for spare parts or legacy product support.

When to Consider Redesigning Instead of Converting

Sometimes conversion isn’t the best approach. Consider redesigning from scratch when:

Scenario	Recommendation
Original design is poorly documented	Redesign may be faster
Component footprints are obsolete	Update to current parts
Design rules violate modern capabilities	Optimize for current manufacturing
Multiple conversion errors	Recreate from schematics
Significant design changes needed anyway	Fresh design more efficient

The time invested in troubleshooting problematic conversions can exceed the time needed for a clean redesign, especially for simpler boards.

Resources for Working with Legacy Gerber Files

Official Documentation

• Ucamco Gerber Specification: ucamco.com/gerber – Current Gerber format specification
• RS-274X User Guide: Historical reference available from Ucamco

Software Downloads

• GerbView: gerbview.com – Commercial converter with free trial
• Gerbv: gerbv.github.io – Free RS-274X viewer
• Reference Gerber Viewer: ucamco.com – Official Ucamco viewer

Aperture Format References

• Standard aperture shapes: Circle, Rectangle, Obround, Polygon
• D-code numbering: Typically D10-D999 (D01-D03 reserved for operations)
• Common wheel file formats: Various vendor-specific formats

Frequently Asked Questions

Why can’t I just use RS-274D files with modern manufacturers?

Most modern PCB manufacturers and their CAM systems expect RS-274X (Extended Gerber) files. RS-274D files require manual intervention to load aperture tables and configure format settings, which introduces errors and delays. Many manufacturers will simply reject RS-274D files and request RS-274X instead.

What if I don’t have the aperture file for my RS-274D data?

Without the aperture file, you’ll need to recreate it. This involves examining the design documentation, measuring features on existing boards, or making educated guesses based on standard pad sizes. It’s tedious but possible. Some CAM software can suggest aperture sizes based on the coordinate data patterns.

Can I convert RS-274X back to RS-274D?

Yes, but why would you? The only reason might be to interface with extremely old equipment. The process involves extracting aperture definitions to a separate file and stripping the header parameters. Some forum posts mention using CAM tools for this, but it’s rarely necessary.

Is RS-274D still used anywhere?

While officially revoked in 2014, RS-274D files still exist in archives and legacy systems. Some very old CAD software may only export RS-274D. However, no modern workflow should generate RS-274D, and any such files should be converted immediately upon receipt.

What’s the difference between RS-274X, X1, X2, and X3?

RS-274X and X1 are essentially the same thing (Extended Gerber without attributes). X2 adds metadata attributes for layer identification and other information. X3 adds component and assembly information. All are backward compatible. Your converted RS-274D files become RS-274X/X1, which can be upgraded to X2 or X3 if your software supports adding attributes.

Conclusion

Converting Gerber RS-274D to RS-274X isn’t complicated once you understand the fundamentals. The key is having all the pieces: the original Gerber files, the aperture definitions, and the correct format settings. With the right software tool, the actual conversion takes just minutes.

The real challenge is often finding or reconstructing missing aperture information. If you’re working with legacy data, take time to locate and preserve aperture files alongside the Gerber files. Future engineers will thank you.

RS-274D served the industry well for decades, but its time has passed. Every RS-274D file you convert to RS-274X is one less potential headache in your manufacturing workflow. The self-contained nature of Extended Gerber eliminates entire categories of errors that plagued the industry for years.

If you’re still generating RS-274D files from legacy CAD software, consider upgrading. Every modern PCB design tool supports RS-274X export, and many support the even newer X2 and X3 formats. The investment in updated software pays for itself quickly in reduced errors and smoother manufacturing handoffs.