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Understanding Thermal Printer DPI

If you've ever tried to scale a barcode to fit on a small label you've probably been met with frustration. If you don't respect the limitations of the printer, you'll end up with "failed" barcodes that will not scan. Software like Label LIVE can help by preventing you from breaking the barcode, but you might still end up being limited by your printer's DPI.

Thermal Printers Print Dots

Thermal label printers create images using small dots. The quality is measured by how many dots fit in one inch (25.4mm), commonly known as DPI. The industry has standardized on 200 and 300 DPI. Why should you consider one over the other? A higher DPI will yield higher quality, but more dots means more flexibility, especially with scaling small barcodes.

The Humble UPC

A UPC stands for "Universal Product Code" and is the standard in retail barcoding. Generally, UPC standards require the UPC barcode to be at least ~1.5" wide for reasons you will soon see. In this example, we will push the limits of the UPC to show differences in 200 vs. 300 DPI.

Demonstrating 200 DPI

Using Label LIVE, we put together a few "tiny" label designs measuring 1" wide and 0.5" tall. First, we demonstrate the smallest UPC barcode possible using 200 DPI, where the narrowest bars are exactly 1 "black" dot wide, and separated by exactly 1 "white" dot.

The blue background shows each individual dot.

Since it is physically impossible for the printer to print anything other than 1 dot at a time, the next "size up" from this barcode means we have to represent the narrowest bar with 2 dots.

Ah! The size!

Now our barcode hangs off the label's edge. We have a few options...

  1. Find a larger label (not a bad idea)

  2. Create our own value text below the barcode (example) and run the risk of the barcode being printed too close to the edge, or not having enough "quiet zone" on the outside of the barcode.

  3. Use a 300 DPI printer

Demonstrating 300 DPI

Again, we use Label LIVE to print the same 1" wide and 0.5" tall label. Here's the same design at 300 DPI, where, just like the first image above, the narrowest bars are exactly 1 "black" dot wide, and separated by exactly 1 "white" dot.

Note how small this barcode is. It's the "same" dot pattern – effectively shrunk because it's built with smaller dots. In reality, it's probably "too small" to be reliably scanned. Let's try the next size up.

Ahhh, perfect! The size doubled but since we started smaller, the doubling gives us a great result.

Let's take a closer look at the dots. Yep, the same pattern as before and everything fits properly.

Summary

These examples demonstrate how a 300 DPI printer can give you more flexibility in managing the size of barcodes on your label design. This is why the 300 DPI mydpi printer is our recommended printer.

The same dot limitations apply to every other barcode type. And remember, if you're actually printing UPC barcodes you should aim to have a minimum width of 1.5" (per the UPC spec).

Happy printing!

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