You have a mailing list ready and a postcard design in the queue, but the size options on the order page read A6, A5 and DL. Those are postcard sizes in millimeters, and the USPS measures in inches. The print size and the postal classification are two separate questions, and they are easy to mix up.
This guide puts the three sizes we print in inches, lines them up against the USPS postcard and letter-size windows, shows what the address side needs, and walks through the checks to run before you commit to a mail run. Nothing here says a card qualifies for a postage rate, because thickness is the variable you still have to verify.
The short version
- A6 is 5.83 x 4.13 inches, A5 is 5.83 x 8.27 inches, DL is 3.90 x 8.27 inches.
- The USPS postcard size window is a minimum of 3.5 x 5 inches and a maximum of 4.25 x 6 inches, 0.007 to 0.016 inch thick.
- A6 fits inside that window by dimensions. A5 and DL exceed it and fall into the letter-size range.
- Thickness is the second test and Paperlust does not publish a caliper for either stock, so measure a sample or ask the Post Office.
- Leave the lower right corner strip clear, except for a light backdrop.
- Mailing rules change, so check the current pages on USPS Postal Explorer before every mail run.
Postcard sizes we print: A6, A5 and DL
Paperlust Print Shop prints postcards on the US pages in three sizes, in color on both sides, priced in US dollars. The table below gives each size in millimeters and inches, and the two stock options available.
| Size | Millimeters | Inches | Paper |
|---|---|---|---|
| A6 | 148 x 105 mm | 5.83 x 4.13 inches | 350 GSM Artboard or 340 GSM Luxe |
| A5 | 148 x 210 mm | 5.83 x 8.27 inches | 350 GSM Artboard or 340 GSM Luxe |
| DL | 99 x 210 mm | 3.90 x 8.27 inches | 350 GSM Artboard or 340 GSM Luxe |
Those are the only postcard dimensions available. There is no 4 x 6 inch or 6 x 9 inch option. If you are building a card for a US mailing list, one of these three sizes is where it starts. You can see current stock and pricing on our postcards page, which also lists the die cut option in the same three sizes and stocks.
USPS postcard size: the window and the letter-size range
The USPS defines two size windows that matter here. A card that fits the postcard window by length and width still has to pass a thickness test. A card that exceeds the postcard window is not rejected; it is simply charged the letter price. The table below shows both windows as listed on USPS Postal Explorer, read on October 15, 2026.
| Mail type | Smallest | Largest | Thickness |
|---|---|---|---|
| Postcard price (First-Class Mail) | 3.5 x 5 inches | 4.25 x 6 inches | 0.007 to 0.016 inch |
| Letter-size | 3.5 x 5 inches | 6.125 x 11.5 inches | 0.007 to 0.25 inch |
A piece below the minimum size of 3.5 x 5 inches cannot be mailed at all. Commercial mailers have a larger postcard allowance of up to 6 x 9 inches under their own rules, but that is a separate track from the standard First-Class Mail postcard price.
A6 postcard: where it sits and why thickness is the second test
By dimensions alone, the A6 card at 5.83 x 4.13 inches sits inside the 4.25 x 6 inch postcard maximum. The A5 card at 5.83 x 8.27 inches and the DL card at 3.90 x 8.27 inches are both longer than 6 inches, which puts them over the postcard size and inside the letter-size limits. So on size, only the A6 postcard clears the postcard window.
But size is not the whole test. The USPS also requires a thickness between 0.007 and 0.016 inch for the postcard price. Paperlust does not state a caliper for 350 GSM Artboard or 340 GSM Luxe, and GSM weight does not tell you the finished thickness. Check the thickness of a printed card or ask the Post Office before you plan a mail run around the postcard rate. This article makes no claim that any size qualifies for a postage price, and it quotes no postage prices.
For the full layout and mailing breakdown, use the A6 postcard size guide.
Address side: what goes where and the four layout steps
The side that carries the delivery address also carries the postage and the return address. Where your address side has a vertical divider, the right panel needs 2.125 inches of width. Where it has a horizontal divider, the lower panel needs 1.5 inches of height. The lower right scan strip runs 4.75 inches inward from the right edge and rises 0.625 inch from the bottom edge, and only a light backdrop may appear there.
Four layout steps to follow before you lock the file:
- Mark the address panel: 2.125 inches wide for a vertical division, or 1.5 inches high for a horizontal division.
- Reserve space within that panel for the postage and the return address alongside the delivery address.
- Leave the 4.75 inch by 0.625 inch corner strip open, allowing only a light print.
- Confirm the delivery address, postage position and return address all fit inside the marked panel before you send the file to print.
Barcode clear zone: what it takes and what it leaves
The barcode clear zone is a lower right strip, 4.75 inches across and 0.625 inch high, starting at the right and bottom edges. On a landscape A6 card that is 5.83 inches wide, the clear zone takes 4.75 of those 5.83 inches along the bottom 0.625 inch, leaving about 1.08 inches at the left of that strip. That 1.08 inches is where any remaining design or text can live in the bottom band.
Keep your message, logos and background graphics out of that corner strip entirely. A light print is acceptable, but anything that competes with the barcode scan will not read reliably.
For the file setup, artwork extends 3 mm (about 0.12 inch) beyond the trim on every edge and text sits 3 mm or more inside the trim. Files go in as a print-ready PDF, SVG or Adobe Illustrator file. A proof is emailed after ordering and nothing prints until you approve it.
If your design calls for die cut postcards with a custom shape, that is a design choice aimed at handouts. Before you mail a die cut card, check with your local Post Office that the shape passes their machinability rules, because a custom cut changes the profile of the piece and the rules that apply.
Mailing checks: six points to confirm before you send
Run through this list before you commit to a mail run. The points below cover size, thickness, layout and current rules.
- Confirm the card dimensions fall inside the USPS postcard window (a floor of 3.5 x 5 inches, a ceiling of 4.25 x 6 inches) or plan for the letter-size classification.
- Measure the thickness of a printed sample against the 0.007 to 0.016 inch postcard range, or ask the Post Office to confirm the caliper for your stock.
- Check the address side layout: address panel width or height, postage and return address space, and the reserved corner strip.
- Verify the reserved corner strip has no text, logos or graphics, with only a light print allowed.
- Confirm the current rules on USPS Postal Explorer, because mailing requirements change and the figures in this guide reflect the pages read on October 15, 2026.
- If the piece is letter-size rather than postcard, note that machinability rules covering shape, stiffness and aspect ratio also apply, and this guide does not give figures for them.
Use the proof step as your last gate. A proof is emailed after you order, and nothing prints until you approve it. Check the trim, the 3 mm bleed beyond the edge and the 3 mm safe area one last time. Before you send the file, use the design a postcard guide for layout setup.
If you are also printing flyers or letters that go in an envelope, the A4 vs Letter guide covers the dimensions and setup for those formats.
Frequently asked questions
What is a standard postcard size in the US?
The USPS defines the postcard price window as a rectangular card with a floor of 3.5 x 5 inches and a ceiling of 4.25 x 6 inches, with a thickness of 0.007 to 0.016 inch. A card outside that window is charged the letter price. This guide does not state that any specific printed card qualifies for the postcard rate, because thickness is the variable you need to verify with a sample or the Post Office.
Is an A6 postcard within the USPS postcard size?
By dimensions, yes. The A6 card is 5.83 x 4.13 inches, which sits inside the 4.25 x 6 inch postcard maximum. But size is only the first test. The USPS also requires a thickness between 0.007 and 0.016 inch, and Paperlust does not publish a caliper for 350 GSM Artboard or 340 GSM Luxe. Measure a printed card or ask the Post Office before you count on the postcard rate for a mail run.
Can I mail an A5 card as a postcard?
No, not by size. The A5 card is 5.83 x 8.27 inches, which is longer than the 6 inch postcard maximum. That puts it in the letter-size range, where the limits go up to 6.125 x 11.5 inches and 0.25 inch thick. You can still mail it, but it will be charged the letter price rather than the postcard rate.
How thick does a postcard need to be?
The USPS sets the postcard thickness floor at 0.007 inch and the ceiling at 0.016 inch. Paperlust has not provided a caliper for either 350 GSM Artboard or 340 GSM Luxe. GSM weight alone does not reveal the finished thickness. Measure a printed card with a caliper or have the Post Office confirm before you rely on the postcard rate.
What goes on the address side of a postcard?
The address side carries the delivery address, the postage and the return address. A vertical split puts the address panel on the right, and it needs 2.125 inches of width. A horizontal split places the panel lower, and it needs 1.5 inches of height. The lower right corner zone, 4.75 inches from the right edge and 0.625 inch from the bottom, allows only a light backdrop.
Do you print 4 x 6 inch postcards?
No. The postcard sizes available on the US pages are A6 at 5.83 x 4.13 inches, A5 at 5.83 x 8.27 inches and DL at 3.90 x 8.27 inches. There is no 4 x 6 inch or 6 x 9 inch option. If you need a card close to 4 x 6, the A6 postcard is the nearest match in both width and height.
