GBL File

What are GBL files and how to open them

Are you having problems opening a GBL file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your GBL files.

What is a GBL file?

A .GBL file is a Gerber Bottom Layer file.

Gerber Bottom Layer File (.GBL) is a standard output from printed circuit board (PCB) design tools that represents the copper features (traces, pads, fills) on the bottom (underside) surface of a two-sided or multilayer PCB. It is produced during the board layout stage and is used by PCB fabrication equipment - photoplotters or CAM systems - to define what copper will remain on the bottom of the finished board.

This file is created when exporting the artwork from electronic design automation (EDA) or CAD software into the Gerber format, typically using the RS-274X (Extended Gerber) or Gerber X2 standard. Once fabricated, this bottom-layer image is combined with others such as solder masks, sinterscreens, and drill files to assemble the full set of manufacturing files required to make the board. A PCB manufacturer uses it directly to generate photomasks that define copper patterns during production.

Internally, .GBL files follow the Gerber RS-274X syntax: they are human-readable ASCII text consisting of commands that define apertures (shapes for drawing), coordinate formats, units (millimetres or inches), and graphic primitives such as moves, draws, and flashes. If in X2 format, attribute blocks such as %TF.FileFunction,Copper,Bot,…% are included near the start to explicitly declare that this file is the bottom copper layer. The file ends with an M02* command indicating end-of-file.

How to open GBL files

We have identified one GBL opener that is compatible with this specific type of GBL file.

Programs that open Gerber Bottom Layer files

Last updated: August 6, 2026

Various apps that use files with this extension

These apps are known to open certain types of GBL files. Remember, different programs may use GBL files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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