Free Online Code 39 Barcode Image Generator
Generating & Printing Code 39 Barcode Images Online Free
Online Code 39 Generator is developed based on OnBarcode
Barcode for .NET.
NOTE
We are providing free online streaming barcode generation service. Now you can
generate barcode image through the following url:
http://generator.onbarcode.com/linear.aspx?TYPE=4&DATA=123456789
To get this free online service, please contact us support@onbarcode.com
Watch a quick video tutorial and get started
Online Barcode Generator Supporting Bar Code Types
OnBarcode barcode products
OnBarcode also provides the following libraries and components for generating, printing, scanning, and reading Code 39 barcodes.
Barcode Software & Libraries
OnBarcode provides professional barcode software and libraries for you.
QR Code Software & DLLs
OnBarcode provides reliable & mature QR Code software and dlls for you.
Code 39 Software & Components
OnBarcode provides other Code 39 barcode generator library, component and SDK for you.
- Code 39 in .NET - how to create 3 of 9 barcode in C#, VB.NET projects with sample codes.
- Code 39 in Java - how to generate best Barcode 3 of 9 1D barcode images in Java projects with examples.
- Code 39 in C# - how to print Code 39 barcodes in C# ASP.NET, C# Excel & word using C# sample codings.
- Code 39 in VB.NET - how to generate Code 39 barcodes in Visual Basic .NET applications with VB.NET samples.
How to Generate free Code 39 Barcode online?
This professional guide fully explains the complete process of generating and customizing Code 39 (a standard linear barcode symbology) in online web browser-based projects. It covers core barcode creation workflows, dual encoding modes, check digit configuration, dimension customization, and critical web project settings.
Code 39 Barcode Data Encoding Online
Code 39 supports two official encoding modes for web applications: Standard Mode and Full ASCII Mode, with unified web-based configuration rules.
Code 39 Standard Mode
Standard Mode supports 43 valid characters, optimized for basic online web browser barcode scenarios.
Supported character set:
- Numeric digits: 0 - 9
- Uppercase letters: A - Z
- Special characters: -, $, %, space, ., /, +
- Dedicated start/stop control characters
For web project implementation, set the barcode type property to "CODE 39".
Code 39 Full ASCII Mode
- Full ASCII Mode supports the complete 128-character ASCII set (ISO 646 IRV), for advanced online web application requirements.
- This mode extends encoding capabilities for lowercase letters and special symbols in browser-based projects.
- For web project implementation, set the barcode type property to "CODE 39 extension".
Note: Select the mode based on your online web project's character needs; using unsupported characters will cause barcode generation failure in the browser.
Code 39 Barcode Check Digit Configuration for Web Projects
Default Check Digit Rule
- Code 39 barcodes do not include a check digit (checksum) by default in standard web implementations.
- For high-security online web applications, enable the MOD43 (modulo 43) check digit for data validation.
Enable Check Digit in Web Projects
- Set the "Add check sum digit" property to true to add the MOD43 check digit to the barcode.
- This enhances data accuracy for online web browser-based barcode scanning.
Hide Check Digit in HRI
- HRI (Human Readable Interpretation): the text displayed below the barcode in web browsers.
- Set the ShowCheckSumChar property to false to hide the check digit in HRI while retaining it for validation.
Code 39 Barcode Start/Stop Characters in Web Browsers
- Code 39 uses the asterisk (*) as the fixed start and stop character for barcode scanning.
- The asterisk (*) cannot be included in the custom barcode data for online web projects.
- Control the display of start/stop characters in web browsers via the ShowStartStopInText property.
- Set to false: Hide the * character in the HRI text
- Set to true: Display the * character in the HRI text
Note: Never add * to the Data property; the online barcode application auto-generates it for web barcode scanning compatibility.
Code 39 Barcode Dimension Customization in Online Web Projects
Customize Code 39 barcode size to fit online web browser UI and responsive design requirements using these core properties:
- UOM (Unit of Measure): Measurement unit for web rendering; supports PIXEL, CM, INCH (PIXEL recommended for browsers).
- X: Width of the narrow barcode module; minimum value defined by web application specifications.
- Y: Height of the barcode module; adjusted for web page display clarity.
- N: Wide-to-narrow module ratio; valid range 2.0 - 3.0 (critical for web scanning compatibility).
- I: Intercharacter gap width; minimum value equals X, with web-specific maximum limits.
- LeftMargin/RightMargin: Quiet zone for web browsers; minimum width = 10X to ensure scanning.
Note: Use PIXEL as the UOM for online web projects; other units may cause display distortion in browsers.
Advanced Customization for Web Browser Code 39 Barcodes
Optimize barcode appearance for online web projects using two core advanced properties:
Wide/Narrow Bar Ratio (N Property)
- Defines the width ratio between wide and narrow barcode modules.
- Valid range: 2.0 - 3.0; default value = 2.0 for web compatibility.
- Adjust for better scanning and display in online web browsers.
Intercharacter Space (I Property)
- Defines the gap between two barcode characters in web rendering.
- Value is a multiple of the X (narrow module width); default = 1.0f.
- Optimize spacing for responsive web browser layouts.
