Barcode Generator

About Barcode Generator

How Barcodes Encode Data

A 1D barcode represents data as a series of parallel bars and spaces of varying widths. A laser or camera scanner measures the widths in sequence, converts them back to numbers, and maps those numbers to characters using the symbology's lookup table. Each format has its own encoding rules, a required start and stop pattern, and usually a checksum so scanners can detect damaged or misread codes.

Worked example (UPC-A check digit for 04210000526): Multiply odd-positioned digits (from the left, 1-indexed) by 3 and even-positioned digits by 1: (0x3)+(4x1)+(2x3)+(1x1)+(0x3)+(0x1)+(0x3)+(0x1)+(5x3)+(2x1)+(6x3) = 0+4+6+1+0+0+0+0+15+2+18 = 46. The check digit is the number that brings the total to the next multiple of 10, so (10 - (46 mod 10)) mod 10 = 4. The complete barcode is 042100005264.

Supported Barcode Formats

Format	Characters Supported	Length	Common Uses
Code 128	All 128 ASCII characters (letters, numbers, symbols)	Variable	Shipping labels, logistics, general-purpose barcodes
Code 39	A-Z, 0-9, space, - . $ / + %	Variable	Automotive, defence, government ID badges
EAN-13	Digits only (0-9)	13 digits (12 + 1 check digit)	International retail products, books (ISBN)
UPC-A	Digits only (0-9)	12 digits (11 + 1 check digit)	North American retail products

How to Use the Generator

Step	Action
1. Choose format	Select the barcode type that matches your use case
2. Enter data	Type or paste the value to encode (the tool validates input in real time)
3. Adjust settings	Set bar height and toggle text display below the barcode
4. Preview	The barcode renders instantly as you type
5. Export	Copy the SVG code or download as a 2x resolution PNG

Which Format Should You Use?

Scenario	Recommended Format	Why
Shipping labels	Code 128	Compact encoding, supports all ASCII characters, universally scanned
Inventory asset tags	Code 128 or Code 39	Code 128 for mixed data; Code 39 for simple alphanumeric IDs
Retail product (worldwide)	EAN-13	Required by retailers outside North America; also encodes ISBNs
Retail product (US/Canada)	UPC-A	Standard for North American point-of-sale systems
Library books	Code 39 or Code 128	Many library systems use Code 39 for patron and item barcodes
Event tickets	Code 128	Can encode alphanumeric ticket IDs efficiently

Check Digit Calculation

EAN-13 and UPC-A barcodes include a check digit as the final character. This digit is calculated from the preceding digits using a weighted sum formula and catches single-digit errors and most transposition errors during scanning. When you enter your data digits, this tool calculates and appends the correct check digit automatically - you do not need to calculate it yourself.

Format	You Enter	Tool Outputs	Check Digit Method
EAN-13	12 digits	13-digit barcode (12 + check)	Alternating weights of 1 and 3, mod 10
UPC-A	11 digits	12-digit barcode (11 + check)	Alternating weights of 3 and 1, mod 10
Code 128	Any text	Barcode with built-in checksum	Weighted modular sum
Code 39	Alphanumeric text	Barcode (optional check digit)	Modulo 43 sum

1D Barcodes vs QR Codes

Feature	1D Barcode (this tool)	QR Code
Data capacity	~20-80 characters	Up to ~4,296 characters
Data types	Primarily text and numbers	URLs, text, WiFi credentials, vCards, any binary data
Scanning direction	Horizontal only - scanner must align with bars	Any angle - reads in all orientations
Physical size	Wide and short	Compact square
Scanner compatibility	Laser and CCD scanners (retail, logistics)	Smartphone cameras and image-based scanners
Industry standard	Retail POS, shipping, manufacturing	Marketing, mobile apps, contactless sharing

Printing and Sizing Tips

Tip	Why
Use the 2x PNG for print	Higher resolution produces sharper bars at small sizes
Maintain quiet zones	Leave blank space on either side of the barcode (at least 10x the narrowest bar width)
Do not stretch horizontally	Distorting the bar widths makes the code unscannable
Print on light backgrounds	Dark bars on white/light backgrounds scan most reliably
Test before bulk printing	Scan a test print with your actual scanner to confirm readability

Common Mistakes When Generating Barcodes

Mistake	What Goes Wrong	How to Avoid It
Printing too small	Bars blur together and the scanner cannot resolve narrow bars from wide ones	GS1 recommends a nominal X-dimension (narrowest bar) of 0.33 mm for retail POS, with a minimum of 0.264 mm. For supply chain barcodes the minimum is 0.495 mm.
No quiet zone	Scanner cannot find the start and stop patterns, so the read fails or decodes partial data	Leave blank margin of at least 10x the narrowest bar width on both sides. For EAN-13 this is typically 7 modules left and right.
Stretched horizontally	Bar widths no longer match the ratios the symbology requires, breaking the decode	Always scale proportionally. If you need a different size, regenerate the barcode rather than stretching the image.
Wrong contrast	Low print contrast between bars and background causes scanners to misread or reject the code	Print black bars on white, cream, or very light backgrounds. Avoid red backgrounds - many red laser scanners read red bars as spaces.
Reusing another company's GS1 prefix	Products collide with an existing GTIN at retail	Only use EAN-13 or UPC-A codes that your company has been assigned by GS1. For internal use, a different symbology (Code 128 or Code 39) is safer.
Embedding special characters in Code 39	Generator rejects the input because Code 39 only supports a limited character set	Switch to Code 128, which encodes any printable ASCII character including lowercase letters and punctuation.

Which Barcode Is Used Where?

Industry	Typical Symbology	Why
Grocery and general retail (worldwide)	EAN-13	Assigned and managed by GS1 member organisations in over 110 countries. The first 2-3 digits identify the GS1 prefix, the next block identifies the brand owner, and the remainder identifies the product.
North American retail	UPC-A	The original 12-digit symbol adopted in 1974 with the first retail scan of a pack of Wrigley's gum. UPC-A is a subset of EAN-13 with an implied leading zero.
Books and periodicals	EAN-13 (ISBN/ISSN)	ISBNs have been encoded as 13-digit EAN barcodes since 2007. The prefix 978 or 979 identifies a book, and the check digit follows the standard EAN-13 rule.
Healthcare and pharmaceuticals	GS1-128 (Code 128 variant)	Encodes GTIN plus batch, expiry, and serial using GS1 Application Identifiers. Required by the EU Falsified Medicines Directive and the US Drug Supply Chain Security Act.
Shipping and logistics	Code 128 (SSCC-18)	GS1 Serial Shipping Container Code encoded as Code 128 for pallet tracking. Dense encoding keeps the label small.
Automotive and defence	Code 39	Adopted by the US Department of Defense (LOGMARS) and the Automotive Industry Action Group. Self-checking, does not require a checksum, simple scanner electronics.
Libraries	Code 39 or Codabar	Many older library management systems still use Code 39 for patron cards and item labels. Newer systems moved to Code 128 for density.

How the Check Digit Catches Errors

The Mod 10 check digit used by EAN-13 and UPC-A is designed to catch the most common keying and scanning errors. It always detects any single-digit error (typing one digit wrong) and detects around 90 percent of two-digit transposition errors. It does not catch every transposition - swapping two digits of equal weight (both odd-position or both even-position) can produce the same checksum - but it is effective enough to keep false reads from propagating into retail databases. Code 128 uses a different scheme, a modulo 103 weighted checksum calculated across every encoded value, which is even stronger because the weighting is linear rather than alternating.

Quiet Zones and Print Resolution

The quiet zone is the blank margin around a barcode that tells the scanner where the symbol begins and ends. GS1 specifies a minimum quiet zone of 7 modules (seven narrow-bar widths) on the left and right of every EAN-13 barcode. Omitting quiet zones is the most common reason retail barcodes fail at checkout - the bars scan fine, but the scanner cannot find the start pattern. For Code 128 the rule is 10 times the narrowest bar on each side, and for Code 39 it is 10 times the narrowest bar or 0.25 inches, whichever is greater.

Print resolution matters more than most people realise. A 300 dpi laser printer produces bars with an edge jitter of roughly 0.08 mm, which is fine for retail EAN at the nominal size but can fail at 80 percent magnification. Thermal transfer printers at 203 dpi are the industry standard for shipping labels because the dot placement is more consistent. Ink-jet printers often struggle because ink bleed widens the dark bars, narrowing the spaces, and a scanner calibrated for the nominal ratios rejects the decode. If you are printing at high volume, test the output with the actual scanner model rather than relying on a smartphone app that is often more forgiving than industrial hardware.

Barcode or QR Code: Which Should You Use?

1D barcodes remain dominant in retail point-of-sale and high-speed logistics because laser scanners are inexpensive, fast, and reliable. QR codes are better when you need to encode URLs, WiFi credentials, payment data, or more than around 80 characters. For most consumer-facing uses like restaurant menus, marketing posters, or contactless sharing, use the QR Code Generator. For inventory and retail tags, stick with 1D barcodes from this tool. For generating unique identifiers to encode, the UUID Generator creates RFC 4122 compliant IDs that pair well with Code 128. For shorter random strings, the Password Generator can produce alphanumeric tokens that fit in Code 39.

All encoding happens in your browser. No input is ever sent to a server, which makes this tool safe for confidential asset tags, internal part numbers, and pre-release SKUs.

Sources

• GS1 - Barcode standards and specifications
• GS1 - EAN/UPC barcode family
• ISO/IEC 15417:2007 - Code 128 specification
• ISO/IEC 16388:2007 - Code 39 specification
• GS1 General Specifications (PDF)
• International ISBN Agency - ISBN on EAN-13