UPC / EAN Barcode Generator

Barcode Generator Guide

What is a Barcode?

A barcode is a machine-readable optical label that encodes data as a pattern of parallel bars and spaces of varying widths. When a barcode scanner or camera passes over it, the reflected light translates the bar pattern back into a digital string. Barcodes are the backbone of retail checkout, warehouse inventory, shipping labels, event ticketing, and asset tracking. They let a computer identify a product or record instantly without manual typing, which is faster and eliminates human error.

Barcode Formats Explained

This generator supports four major barcode symbologies, each designed for different use cases:

• UPC-A (Universal Product Code): 12 digits, the retail standard in the United States and Canada. Encodes a manufacturer prefix (first 6-10 digits), an item reference, and a check digit. Every product sold in North American retail stores needs a UPC-A barcode registered with GS1 US.
• EAN-13 (European Article Number): 13 digits, the global retail standard used everywhere outside North America. Structurally identical to UPC-A with an extra digit prepended. The first 3 digits are the GS1 country prefix, followed by the manufacturer code, product code, and a check digit. An EAN-13 starting with 0 is functionally equivalent to a UPC-A.
• Code 128: A high-density linear barcode that can encode all 128 ASCII characters, including letters, numbers, and symbols. Used for shipping labels, packaging, and internal inventory where alphanumeric codes are needed. It is the standard for GS1-128 shipping container labels and is widely used by FedEx, UPS, and DHL.
• Code 39: An older linear format encoding 43 characters (A-Z, 0-9, and 7 special characters). It is less dense than Code 128 but still widely used for asset tags, library cards, and industrial labeling where letter encoding is needed but full ASCII is not required.

Check Digit Calculation

The last digit of UPC-A and EAN-13 barcodes is a check digit, computed from the preceding digits using the modulo-10 algorithm. This allows scanners to detect misreads. The formula works as follows: starting from the rightmost digit (excluding the check digit), multiply odd-position digits by 3 and even-position digits by 1. Sum all products. The check digit is the number that makes this sum a multiple of 10.

For example, for the 12-digit UPC-A code 036000291452: the first 11 digits are 0-3-6-0-0-0-2-9-1-4-5. Applying the weighted sum: (0+6+0+0+2+1+5)x3 + (3+0+0+9+4) = 42 + 16 = 58. The next multiple of 10 after 58 is 60, so the check digit is 60 - 58 = 2. This tool automatically calculates the check digit for you when you enter the first 11 or 12 digits.

How to Use This Generator

Select your barcode format from the dropdown. Enter the data to encode: 11 or 12 digits for UPC-A, 12 or 13 digits for EAN-13, or any alphanumeric string for Code 128 and Code 39. Adjust the bar width, height, and whether to display human-readable text below the bars. The preview updates in real time. Click Download to save the barcode as a high-resolution PNG image suitable for printing on product packaging or labels.

GS1 Registration and UPC/EAN Prefixes

If you are creating barcodes for retail products sold in stores or on marketplaces like Amazon, you cannot invent your own numbers. You must purchase a GS1 Company Prefix from GS1 (gs1.org) or a regional GS1 member organization. The prefix assigns you a unique range of barcode numbers that no other company can use. Amazon, Walmart, Target, and most major retailers require GS1-registered barcodes and will reject self-generated ones. For internal use like warehouse inventory or asset tracking, you can freely use any number with Code 128 or Code 39.

Printing Tips

• Always leave a quiet zone (blank white space) of at least 5 mm on both sides of the barcode so scanners can detect the start and end patterns.
• Print at 300 DPI or higher resolution. Low-resolution printing causes bar edges to blur, leading to scan failures.
• Minimum recommended height is 25 mm for retail barcodes. Shorter bars scan less reliably from an angle.
• Use high-contrast colors: black bars on white background. Never use red, which is invisible to most laser scanners.