Direct thermal shipping labels: sizes, printers and fading

A shipping label has one job. It has to scan at pickup, at the hub and at the customer's door. When it fails, the parcel is still your problem. It sits in a sorting centre while you answer an angry WhatsApp.

Here is the short answer. For most small sellers, a direct thermal label printer with 4x6 inch (100 x 150 mm) labels is the simplest setup. It needs no ink, no toner and no ribbon, and the print lasts long enough for a shipment. Match the label width and the roll core to your printer, keep spare rolls cool and dark, and scan-test a few labels before you print a big batch.

What is the difference between direct thermal and thermal transfer?

Both use heat.

The difference is where the black comes from.

Zebra, one of the big label printer makers, explains it well in its own FAQ on the two methods. Direct thermal uses chemically treated, heat-sensitive paper that turns black where the print head heats it. Thermal transfer uses a heated ribbon that melts ink onto the label. Zebra lists shipping labels, receipts and tickets as typical direct thermal jobs, and keeps thermal transfer for labels that must survive heat, sunlight, chemicals or years of storage.

	Direct thermal	Thermal transfer
How it prints	Heat darkens the label itself	Heat melts ribbon ink onto the label
What you keep buying	Labels only	Labels and ribbons
How long the print lasts	Long enough for a shipment, fades with heat, light and rubbing	Much longer, made for harsh conditions
Best for	Shipping labels, courier slips, short-life barcodes	Product labels, asset tags, outdoor use

We have no tie with Zebra. I am quoting it because its pages are public and clear, and the physics is the same for every brand.

Why do small sellers use direct thermal?

Because the only thing you refill is the label roll.

We sell labels, not printers, so I have no reason to push you towards an expensive machine.

I say the same about any packing machine. The machine is a one-time cost. The consumable is the running cost, and the running cost is what decides your profit per order over a year. With direct thermal, there is no ribbon to buy, no ink cartridge drying up during a slow week, and no ribbon to change at 10 pm in the festive rush.

The maths is simple. One shipping label per parcel. So a seller shipping 300 orders a month uses about 300 labels a month, plus a few for reprints and tests.

A label printer also saves time over printing labels on A4 sheets and cutting them out. That matters more than people think when you pack 40 orders after dinner.

The honest limit, as our own listing says, is that direct thermal print fades with heat and strong sunlight over time. A shipping label needs to last days, not years, so that is usually fine. For a label that must stay readable for months, ask us about other label types.

Which label size do I need?

For courier shipping labels in India, 4x6 inches is the common size. The exact size is 101.6 x 152.4 mm, and most rolls are sold as 100 x 150 mm. The Delhivery One help pages offer a 4x6 inch format for thermal label printers, and an A4 format with four labels on a sheet for desktop printers. Other panels may name the options differently, so look for the thermal or 4x6 setting.

Label size	In mm	What it is for	On our store
4x6 inch	101.6 x 152.4 (sold as 100 x 150)	Courier shipping labels with address, AWB and barcode	See the second label listing below
2x1 inch	50.8 x 25.4	SKU and barcode stickers for products, stock bins and inner boxes	Our 2x1 inch roll, 1000 labels per roll, pack of 2

We have two label listings, and I want to be clear about both.

Our 2x1 inch direct thermal labels come 1000 labels to a roll, in a pack of 2 rolls. A 2x1 inch label is too small for a courier shipping label. It is for marking your own stock, so a swapped return or a wrong-size pick is easy to catch.

Our direct thermal label roll is the one for shipping labels, sold as 1 roll or 2 rolls. Before you order, check the label size and labels per roll on the listing against your printer and the format your shipping panel prints. If anything is unclear, message us and we will confirm it for your printer.

One mistake is very common. A seller downloads the A4 label file from the panel and prints it scaled down onto a 4x6 label. The barcode shrinks with it, and a shrunk barcode is harder to scan. Pick the 4x6 or thermal format in your panel settings instead.

Direct thermal label roll with a printed shipping label

How do I match a label roll to my printer?

Check five things before you order. You will find all of them in the spec sheet or manual of your printer.

The width. The label must fit the media width of the printer. The ZD421 spec sheet from Zebra (2021) gives 15 to 108 mm for the direct thermal model, so a 4 inch label fits. A 2 inch model such as the ZD411d takes media only up to 57 mm, so it can never print a 4x6 label.
The core size. This is the hole in the middle of the roll. The ZD421 takes 0.5 inch and 1 inch cores as standard, and 1.5, 2 and 3 inch cores only with an optional adapter. A roll on the wrong core simply will not sit on the spindle.
The roll diameter. The outside of the roll must fit inside the printer. On the ZD421 the limit is 127 mm (5 inches). Bigger industrial rolls need a bigger printer.
The label type. A direct thermal printer needs direct thermal labels. Plain paper stickers will come out blank, because there is nothing in them to darken.
The gap sensing. After loading a new roll, run the calibration on the printer, so it finds the gap between labels. Skip this and the print drifts across two labels.

Your printer will have its own numbers.

I would always test one roll on your own machine before ordering more. We say the same on our listing. If you are unsure, send us your printer model before you buy, and we will tell you whether our roll fits.

Why do thermal labels fade, or turn black?

Because the coating that darkens under the print head also reacts to other things around it.

Koehler, a German thermal paper maker, lists the factors in its durability note (2022): long exposure above 40°C, damp storage, contact with plasticisers in PVC film, contact with oils, fats and alcohol, aggressive chemicals, direct sunlight, and a weak print from a faulty print head or a wrong printer setting. The care advice from Ricoh for thermal paper adds solvents, rubbing and water to the list.

In an Indian packing room, those turn into very ordinary things:

A roll left on the dashboard of a delivery van, or near a window in May.
A tin-roof godown in summer, where the afternoon heat can cross 40°C.
Hand sanitiser, which is mostly alcohol, on the fingers of whoever is packing.
Oily fingers from lunch, or hand cream.
Printed labels kept for days in a PVC folder or a soft plastic sleeve.

The first two can turn the whole roll grey before you print a single label. The last three fade or smudge the labels you have already printed.

How should I store label rolls?

The Koehler ideal is 18 to 25°C, 40 to 60% humidity and no light. Few Indian godowns hit that in June, so aim for the closest you can manage.

Keep rolls in their wrap until you load them, inside a closed carton.
Store that carton indoors, in a cupboard or a drawer, off the floor and away from windows and walls that heat up.
Do not keep labels in PVC folders or next to cleaning chemicals.
Use the oldest roll first.
Buy about one month of labels at a time. A stock that sits through a whole summer is a stock that slowly greys.

And wash your hands, or let the sanitiser dry fully, before you handle printed labels.

What is a scan test, and why run it before a big batch?

A scan test takes five minutes and can save a full day of dispatch.

I would never skip it before a sale day. Do it whenever you load a new roll or change a setting.

A phone scanning the barcode on a parcel label before dispatch — Photo: RDNE Stock project on Pexels

Print three labels from real orders.
Look at the barcode. The bars should be solid black with clean white gaps. Grey bars mean the print is too light. Bars that run into each other mean it is too dark.
Scan each barcode with the courier app, a barcode app on your phone, or a handheld scanner.
Stick one label on a courier bag and one on a carton, and scan again. A label on soft film can wrinkle, and wrinkles break barcodes.
Rub one label firmly with your thumb and scan it once more.
Adjust the darkness setting on the printer if needed, and only then print the batch.

Where should the label go on the parcel?

On the largest flat face, away from edges, seams and the closing strip. On a courier bag, keep it on the flat front, not across the seal. Our courier bag size chart helps you pick a bag that is not overstuffed, and a flat bag gives the label a flat bed.

The invoice needs its own home. For cartons, put it in a packing list envelope next to the label. For courier bags, use the POD jacket on the bag. If you also want your packing record to stand up in a return dispute, read our guide on tamper-proof courier bags and return fraud. A readable label in the packing video is half of that evidence.

Questions sellers ask

Do I need ink or a ribbon? No. A direct thermal printer prints with heat alone.

Can I print these labels on my inkjet or laser printer? No. Only the heat of a thermal print head darkens them in the right places. They are made for a thermal label printer, and nothing else.

How far ahead can I print labels? Print on the day you ship. A label printed a week early, kept in a warm room, is a label you may have to print again.

If you are setting up your first packing table, our small seller's packing station guide lists what to buy first. And if you are not sure a roll will fit, send us your printer model. We would rather check it with you than have a roll sitting unused in your drawer.