Look closely at a shipping label and you'll usually see two different kinds of code: a long, narrow linear barcode and a square QR-style code. They're not redundant, they do different jobs, and understanding the difference is genuinely useful when you're troubleshooting why a label won't scan or why a parcel got held.
What a linear barcode is
The long barcode made of vertical bars is a linear, or one-dimensional, barcode. On shipping labels it's almost always Code 128, which is the symbology the courier industry standardised on because it packs a lot of data into a compact space and scans reliably at speed. That barcode carries the tracking number and routing data, and it's the one the depot scanners read at every step.
What a QR code is
The square code is a two-dimensional matrix code, and the QR in the name stands for Quick Response. It stores data both horizontally and vertically, so it holds far more than a linear barcode in a small area. On a shipping label, the QR code often carries a link or extra routing information that complements the main barcode rather than replacing it.
Why both appear on one label
The linear Code 128 is the workhorse, optimised for fast, reliable scanning on conveyor belts and handheld scanners. The QR code is the supplement, carrying more data or a readable link for systems that can't use the linear code. Together they give the carrier redundancy and flexibility, which is why a modern label rarely has just one.
Why Code 128 is the shipping standard
Code 128 won the industry because it's dense, meaning lots of data in a small space, and it self-checks, meaning a misread is rare. It's also fast to scan with a simple laser, which matters when a parcel is moving past a scanner at speed. For a tracking number and routing data, it's close to the perfect tool. Our barcode failure guide covers what happens when it doesn't scan.
How print quality affects each
Both codes fail the same way when the print is poor, but they fail at different thresholds. A linear barcode needs clean, distinct bars with enough contrast, so faint or smudged thermal prints are its enemy. A QR code has built-in error correction, so it can survive more damage, but only if the print is dark and sharp enough for the squares to resolve. Either way, a clean thermal print is the fix.
Resolution and why 203 DPI is usually enough
For the large Code 128 on a 100 × 150mm label, a 203 DPI printer prints it perfectly scannable. The QR code is more demanding, and if it's a small, dense QR code with lots of data, a 300 DPI printer starts to matter. For standard shipping labels, 203 DPI handles both fine, which our resolution guide explains.
What to check when a code won't scan
When a label won't scan, the diagnosis order is: is the print dark enough, is the label full size and not scaled down, and is the barcode creased or covered. Most scan failures are a print or handling issue, not a problem with the code itself, and the fixes are almost always a darkness adjustment or reprinting at 100% scale.
Frequently asked questions
What barcode do shipping labels use? The main barcode is almost always Code 128, the courier industry standard, with a QR code often added for extra data or a link.
Why do labels have both a barcode and a QR code? They serve different purposes. Code 128 is the fast-scanning tracking barcode, while the QR code carries more data or a link as a supplement.
Why won't my shipping label barcode scan? Usually print quality or scaling. Check the darkness, print at 100% size, and make sure the barcode isn't creased or covered.
Codes that scan first time
Both the Code 128 and the QR code on a shipping label depend on a crisp print. Our 100 × 150mm direct thermal labels deliver it every time.
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