You print a label from MyPost Business, send it to your thermal printer, and get back a blank page, a tiny stamp crammed into the top corner, or an error. The label file is clearly there. The printer is on. So what's going on?
The short answer: MyPost Business downloaded an A4 PDF, and your thermal printer expects a 100x150mm page. They're speaking different languages.
This is one of the most common frustrations for Australian ecommerce sellers who've just set up a thermal printer, or who've been tolerating the problem for months without knowing why it happens. This post explains the actual reason, then covers every way to fix it.
In this article:
- Why MyPost Business uses A4 format by default
- What the A4 format actually looks like
- Fix 1: Change your label format in MyPost Business settings
- Fix 2: Crop the PDF manually
- Fix 3: Automate the whole thing
- Which fix is right for you?
Why MyPost Business uses A4 format by default
MyPost Business was built to serve a wide range of Australian businesses: post office counters, retail stores, warehouses, and home sellers. When the platform launched, most businesses printed labels on A4 paper using standard office inkjet or laser printers. A4 was the safe default that worked for everyone.
Thermal roll printers, the kind Dymo, Zebra, Brother, and MUNBYN make, were added to the picture later. Australia Post did add support for thermal label output, but they made it an opt-in setting rather than auto-detected. So every new MyPost Business account still defaults to A4 today, even if you're connecting a thermal printer.
It's not a bug. It's a deliberate choice to maximise compatibility across all printer types. The downside is that nobody tells you about it when you sign up, and the fix isn't obvious when you're staring at a blank thermal label wondering what went wrong.
The technical side of it: the label itself (100x150mm) is embedded inside an A4-sized PDF document. Australia Post's system wraps the label in an A4 container so it can be printed at any scale. A laser printer handles this fine because it ignores the excess white space. A thermal printer tries to print the entire A4 page onto a 100x150mm roll and either chokes on the size mismatch or prints the label as a tiny rectangle with a massive white border.
What the A4 format actually looks like
When you download a label from MyPost Business in the default setting, you get a PDF where the actual shipping label sits in the top-left corner of an A4 page. The label content (barcode, address, tracking number, postage class) is correct. The problem is just the surrounding space.
On a normal laser printer loaded with A4 paper, this works. The label prints correctly in the top-left corner, you cut it out (or peel it if you're using A4 label sheets), and it goes on the parcel.
On a thermal printer loaded with 100x150mm roll labels, the printer receives a 210x297mm document and has no idea what to do with it. Different printers respond differently: some scale the whole page down (giving you a tiny label), some try to print at full size and cut off the bottom, some throw an error.
The result is the same: wasted labels, wasted time, and you back at the computer googling why your printer hates Australia Post.
Fix 1: Change your label format in MyPost Business settings
This is the proper fix. Takes about two minutes, and you only need to do it once.
- Log in to your MyPost Business account at auspost.com.au/mypost-business
- Go to Settings in the top-right menu
- Select Carriers, then click MyPost Business
- Under Print Settings, find the label size option
- Change it from A4 to A6 - 1 per page
- Save
From this point on, every label you download will come out as a 100x150mm PDF ready for your thermal printer. No cropping, no resizing, no print dialog gymnastics.
A note on label sizes: Australia Post offers A6 (105x148mm) and 100x150mm as two options. Both work fine for thermal printers. The slight size difference is irrelevant for printing, and neither affects the barcode or postage. Pick whichever your printer lists in its paper size settings.
What if the setting doesn't stick? A handful of sellers report that the setting reverts after a logout. If this happens to you, it's usually a session/cookie issue. Try clearing your browser cache, logging back in, and saving the setting again. If the problem persists, contact Australia Post support.
Fix 2: Crop the PDF manually
If you can't change the account setting (for example, if someone else manages your MyPost Business account and you're only the label-printer), or if you have a backlog of A4 labels you already downloaded, manual cropping is the fallback.
On Mac
- Open the A4 PDF in Preview
- Go to File > Print
- Click Paper Size in the print dialog and choose Manage Custom Sizes
- Create a new size: 100mm x 150mm
- Set all margins to 0mm
- Click OK, then print
Alternatively: In Preview, go to Tools > Rectangular Selection, drag a box around just the label, then use File > Export as PDF to save just the selected area.
On Windows
- Open the PDF in Adobe Acrobat Reader (free version)
- Go to Edit > Take a Snapshot
- Drag a selection box around the label
- Open a new document, paste the snapshot
- Print at 100x150mm
Or use the Crop Pages tool in Adobe Acrobat Pro (paid). It lets you set exact crop dimensions and saves the cropped PDF as a new file.
Using free online tools
PDFsam, PDF24, and Smallpdf all have crop/resize tools that work for this. Upload the A4 PDF, crop it down to the label area, download, and print. Uploading your shipping labels to a third-party server isn't ideal from a privacy standpoint, but it works if you're in a pinch.
The problem with manual cropping: it adds 2-5 minutes per label. Fine for occasional shipping. A slow, annoying grind if you're printing 20 labels a day.
Fix 3: Automate the whole thing
If you're printing more than a handful of labels per day, manual cropping is a real drag. The logical next step is automating it.
The fully automated version works like this: you download labels from MyPost Business the same way you always have, but instead of opening PDFs and fighting with print dialogs, the labels just print. A background app watches your Downloads folder, detects the A4 label PDF the moment it appears, crops it to 100x150mm, and sends it straight to your thermal printer.
This is what LabelChop does. It's a desktop app built specifically for Australian sellers using MyPost Business with thermal printers. You set it up once (choose your watch folder, choose your printer), and it runs quietly in the system tray from then on. Labels go from downloaded to printed in about 3 seconds.
For sellers who've already switched their account settings to A6 but still occasionally end up with A4 labels (from multi-label exports, or when someone else in the business downloads them with the wrong setting), the watch-folder approach is a useful safety net.
If you want to keep things free and don't mind a bit of setup, a Mac app called Hazel can watch your Downloads folder and run an Automator script to crop PDFs. It's not as seamless as a purpose-built tool, but it works.
Which fix is right for you?
If you control your own MyPost Business account and print more than occasionally, the settings change (Fix 1) should be your first move. It's free, it's fast, and it solves the problem permanently for new labels.
If you're already on A6 in your settings but still occasionally get misfires, check that you're selecting the right paper size in your print dialog and that your PDF reader isn't scaling the document to fit.
If you print high volumes daily and want the fastest possible workflow, automation saves real time. Five minutes per label across 30 shipments a day adds up to 2.5 hours. Even cutting that to 30 seconds per label saves most of it.
Related reading:
- How to crop MyPost Business A4 labels to 4x6 — step-by-step cropping guide for all methods
- Print MyPost Business labels on a thermal printer — full thermal printer setup guide
- MyPost Business label setup for eBay and Shopify — connecting your store and configuring print settings
The A4 default in MyPost Business catches nearly every new thermal printer owner off guard. It's a platform quirk that Australia Post hasn't changed in years, and their help pages don't explain it clearly. Now you know why it happens and what to do about it.
Change the setting once and forget about it. Or if you want labels to print the moment they download, give LabelChop a try free for 14 days and see how much time you get back.