What is .kicad_pcb? KiCad PCB File Format Guide

If you’ve worked with KiCad or received board files from someone using the open-source EDA tool, you’ve encountered the .kicad_pcb extension. This is the native file format for KiCad’s PCB editor (Pcbnew), containing everything needed to define a printed circuit board—from copper layers and footprints to design rules and manufacturing settings.

Unlike proprietary binary formats from commercial EDA tools, .kicad_pcb files are human-readable ASCII text using S-expression syntax. This openness is one reason KiCad has gained massive adoption among hobbyists, students, and professional engineers who value transparency and the ability to version-control their designs with Git.

This guide explains what .kicad_pcb files contain, how to open and convert them, and practical tips for working with this format in your PCB design workflow.

What is a .kicad_pcb File?

A .kicad_pcb file is the primary board layout file created by KiCad’s PCB editor. It stores the complete PCB design including copper traces, footprints, vias, zones, design rules, and layer stackup configuration. The format was introduced in KiCad version 4.0, replacing the older .brd format with a more maintainable S-expression structure.

The .kicad_pcb format is UTF-8 encoded ASCII text, which means you can open it in any text editor to inspect or even manually edit the contents. All dimensions are stored in millimeters with nanometer precision, making it suitable for designs ranging from simple two-layer hobby boards to complex 32-layer professional PCBs.

.kicad_pcb File Identification

KiCad Project File Structure

Understanding where .kicad_pcb fits within a KiCad project helps when sharing designs or troubleshooting file issues.

Essential KiCad Project Files

When distributing a KiCad design, you need the .kicad_pro, .kicad_sch, and .kicad_pcb files at minimum. KiCad embeds all referenced symbols and footprints directly into the schematic and board files, so recipients can open your design without needing your custom libraries.

Inside a .kicad_pcb File Structure

The .kicad_pcb format uses S-expressions—a simple nested parenthetical syntax borrowed from Lisp. This structure is both human-readable and easily parsed by software.

Main Sections in .kicad_pcb Files

Example .kicad_pcb Header Structure

(kicad_pcb (version 20221018) (generator pcbnew)  (general    (thickness 1.6)  )  (paper “A4”)  (layers    (0 “F.Cu” signal)    (31 “B.Cu” signal)    (32 “B.Adhes” user “B.Adhesive”)    (33 “F.Adhes” user “F.Adhesive”)    (34 “B.Paste” user)    (35 “F.Paste” user)    (36 “B.SilkS” user “B.Silkscreen”)    (37 “F.SilkS” user “F.Silkscreen”)    (38 “B.Mask” user)    (39 “F.Mask” user)    (40 “Dwgs.User” user “User.Drawings”)    (41 “Cmts.User” user “User.Comments”)    (44 “Edge.Cuts” user)  )    ;; setup, nets, footprints, tracks, zones follow…)

The version number indicates which KiCad release created the file. Files from newer KiCad versions may not open correctly in older versions due to format changes.

KiCad PCB Layer System

KiCad supports up to 32 copper layers plus numerous technical and user layers. The .kicad_pcb file defines which layers are active and their properties.

Standard KiCad Layers

The Edge.Cuts layer is particularly important—KiCad uses graphical objects on this layer to define the physical board outline. Without a valid closed outline on Edge.Cuts, functions like 3D viewing and some DRC checks won’t work correctly.

How to Open .kicad_pcb Files

The primary way to open .kicad_pcb files is with KiCad itself, but several alternatives exist depending on your needs.

Software That Opens .kicad_pcb Files

Opening in KiCad

To open a .kicad_pcb file in KiCad:

1. Launch KiCad and open or create a project
2. Click the PCB Editor (Pcbnew) icon
3. Use File → Open and select your .kicad_pcb file

Alternatively, double-click the .kicad_pcb file directly if KiCad is set as the default application for this extension.

Viewing Without KiCad

Since .kicad_pcb files are plain text, you can open them in any text editor (Notepad++, VS Code, Sublime Text) to inspect the contents. This is useful for scripting, debugging import issues, or understanding what changed between versions when using version control.

Converting .kicad_pcb Files

Converting .kicad_pcb files to other formats—or importing other formats into KiCad—is a common requirement when collaborating with engineers using different EDA tools.

Import Support (Into KiCad)

Export from .kicad_pcb

Converting to Altium Designer

Altium Designer includes an Import Wizard that directly reads .kicad_pcb files:

1. In Altium, select File → Import Wizard
2. Choose KiCad Design Files
3. Select your .kicad_pcb and .kicad_sch files
4. Map layers as prompted
5. Review the migration log for any conversion issues

The conversion typically requires some manual cleanup, but Altium’s importer handles most design elements correctly.

Online Conversion Tools

Generating Manufacturing Outputs from .kicad_pcb

The .kicad_pcb file is your design database, but PCB manufacturers need Gerber files and drill data. KiCad generates these from the Plot dialog.

Gerber Export Checklist

Many PCB manufacturers now accept .kicad_pcb files directly, generating their own Gerbers. This can reduce errors from misconfigured exports. Check with your manufacturer whether they support native KiCad file submission.

Read more PCB Files format:

What are .GBR and .PHO Files? Gerber File Extensions Guide

What are PCB Panelization Files? Complete Array Format Guide

What is .DSN File? Specctra Autorouter Format Explained

What is .kicad_pcb? KiCad PCB File Format Guide

What is .PcbDoc? Altium Designer PCB Format Explained

What is .PrjPcb? Altium Designer Project File Explained

What is .SchDoc? Altium Schematic File Explained

What is a .ASC File? PADS ASCII Format Explained

What is a .BRD File? Eagle PCB File Format Explained

What is a .DRC File? Design Rule Check Reports Explained

What is a .PCB File? Complete Protel/Altium PCB Format Guide

What is a .SES File? Complete Specctra Session File Guide for PCB Engineers

What is a BOM File? Bill of Materials Format for PCB Assembly

What is a CPL File? SMT Component Placement Guide

What is a Fabrication Drawing? PCB Fab Notes Explained

What is a Gerber Job File? Project Metadata Explained

What is a Netlist? PCB Connectivity Data Explained

What is a Pick and Place File? SMT Centroid Data Guide

What is a Stencil Gerber File? Complete Solder Paste Stencil Guide

What is an Aperture File? Gerber Tool Definition Guide

What is an Assembly Drawing? Complete PCB Assembly Documentation Guide

What is DXF in PCB Design? CAD Drawing Exchange Format Explained

What is Excellon? NC Drill File Format for PCB Manufacturing

What is GenCAD? Universal PCB Data Format Explained

What is Gerber RS-274X? The PCB Industry Standard Explained

What is Gerber X2? The Modern Gerber Format Guide

What is Gerber X3? Component Data in Gerber Files

What is HPGL? PCB Plotter File Format Guide

What is IGES? 3D PCB Model Format Explained

What is ODB++? Complete PCB Data Exchange Format Guide

What is PDF/A for PCB? Documentation Standards Guide

What is STEP File in PCB Design? 3D Model Exchange Guide

What is VRML in PCB? 3D Visualization Format Guide

Editing .kicad_pcb Files Programmatically

Because .kicad_pcb files are structured text, they’re amenable to scripting and automation.

Python Scripting with KiCad

KiCad includes Python bindings that allow direct manipulation of PCB data:

python

import pcbnew# Load boardboard = pcbnew.LoadBoard(“mydesign.kicad_pcb”)# Iterate through footprintsfor footprint in board.GetFootprints():    print(f”{footprint.GetReference()}: {footprint.GetPosition()}”)# Save modified boardpcbnew.SaveBoard(“modified.kicad_pcb”, board)

This enables automated tasks like generating panelized boards, updating footprints in batch, or extracting design data for reporting.

Direct Text Manipulation

For simple changes, you can edit .kicad_pcb files directly in a text editor. Common use cases include:

• Changing board thickness in the general section
• Updating title block information
• Bulk find-and-replace on net names
• Fixing minor syntax issues from failed imports

Always back up your file before manual editing, and verify the result opens correctly in KiCad.

Version Compatibility

The .kicad_pcb format has evolved with each major KiCad release. Files from newer versions may not open in older KiCad installations.

KiCad Version History

When sharing designs, specify which KiCad version you used. If collaborators have older versions, consider providing Gerber outputs as a fallback.

Useful Resources for .kicad_pcb Files

Official Documentation

Community Resources

Component Libraries

Frequently Asked Questions About .kicad_pcb Files

Can I open .kicad_pcb files without KiCad installed?

Yes, .kicad_pcb files are plain ASCII text, so any text editor can display the raw content. However, to view the graphical board layout or make design changes, you need KiCad or another EDA tool that supports the format (like EasyEDA or Altium with import). For quick visual inspection without installing KiCad, some online Gerber viewers accept KiCad files, though results vary.

How do I convert .kicad_pcb to Gerber files?

In KiCad’s PCB editor, go to File → Plot. Select your output directory, check the layers you need (typically F.Cu, B.Cu, F.Mask, B.Mask, F.SilkS, B.SilkS, Edge.Cuts), and click Plot. Then click “Generate Drill Files” to create Excellon drill data. Always verify your Gerbers in KiCad’s built-in Gerber Viewer or a standalone viewer before sending to fabrication.

Why won’t my .kicad_pcb file open in an older KiCad version?

The .kicad_pcb format changes between major KiCad releases. Files created in KiCad 7 or 8 contain syntax and features that older versions don’t understand. The solution is either to upgrade to a newer KiCad version, or ask the file creator to export Gerbers or save in a compatible format. KiCad does not provide a “save as older version” option.

Can PCB manufacturers accept .kicad_pcb files directly?

Yes, many manufacturers now accept native .kicad_pcb files and generate Gerbers themselves. This includes popular services like JLCPCB, PCBWay, and Multi-CB. Submitting native files can reduce export errors and allows the manufacturer to optimize settings for their process. However, always confirm with your specific manufacturer what file formats they accept.

How do I fix a corrupted .kicad_pcb file?

Since .kicad_pcb files are text-based, minor corruption is sometimes fixable. Open the file in a text editor and look for obvious syntax errors—mismatched parentheses, truncated lines, or garbled characters. KiCad creates backup files (.kicad_pcb-bak), so check if a recent backup exists. For version-controlled projects, you can also revert to a previous commit. If the file is severely corrupted, you may need to regenerate from schematics or restore from a separate backup.

Conclusion

The .kicad_pcb file format embodies KiCad’s philosophy of openness and transparency. Unlike proprietary binary formats that lock designs into specific tools, the S-expression text format means your PCB data remains accessible, scriptable, and version-controllable indefinitely.

Whether you’re a hobbyist designing your first board or a professional engineer evaluating open-source EDA tools, understanding the .kicad_pcb format helps you work more effectively with KiCad and collaborate smoothly with others in the ecosystem. The format’s readability also makes troubleshooting easier—when something goes wrong, you can often diagnose the issue by examining the file directly.

As KiCad continues gaining professional adoption, the .kicad_pcb format serves as a practical, well-documented standard for PCB design data exchange in the open-source hardware community.