Postcard Size Guide: The 4 × 6 Standard, USPS Minimum and Maximum, and How A6, 5 × 7 and Japan's Hagaki Compare

The standard postcard size is 4 × 6 inches (10.2 × 15.2 cm). It is the size most print shops, photo labs and greeting-card racks default to, and in the United States it sits just inside the postcard price.

For a card to qualify for the USPS postcard price, it must be at least 3.5 × 5 inches and no more than 4.25 × 6 inches, and no thicker than 0.016 inch. Anything larger, such as a 5 × 7 or 6 × 9 card, is mailed as a letter.

Joe got into print sizes through the photo booth business in Taiwan, and the same questions kept coming up: is 4 × 6 the same as A6, can a photo print be mailed as a postcard, and why does a card that mails fine in one country get charged as a letter in another. This guide puts the common sizes and three countries’ postal limits side by side.

Common postcard sizes

Pixels follow one formula: inches × 300 = pixels. A 4 × 6 card needs a file of at least 1,200 × 1,800 px to print sharply; below that it starts to look soft. Printers also ask for bleed, usually about 3 mm (roughly 1/8 inch) on each side, so check your printer’s template before exporting.

The “In the US mail” column follows the USPS size categories: postcards are 5 to 6 inches long and 3.5 to 4.25 inches high, and letters run up to 11.5 inches long and 6.125 inches high. A 6 × 11 card is a letter-size piece, not a postcard.

USPS postcard requirements

Source: USPS Postal Explorer, “What Are You Mailing? Domestic” and DMM 201, physical standards, checked October 18, 2026.

Two practical consequences. First, a standard 4 × 6 card is inside the postcard range, which is why it is the default. Second, the popular direct-mail sizes 6 × 9 and 6 × 11 look like postcards but are letters to USPS, so they pay the letter price. If the goal is the cheapest stamp, stay at or under 4.25 × 6.

Is A6 the same as 4 × 6?

No, but they are close enough to be confused. A6 is an ISO paper size (10.5 × 14.8 cm) used across Europe and Asia; 4 × 6 is an inch-based photo size (10.16 × 15.24 cm).

The areas differ by less than 1 cm², so side by side they look the same size. The difference is the shape: 4 × 6 is a little longer and narrower, A6 a little wider and shorter. A design made for one will need re-cropping for the other, and a 4 × 6 photo in an A6 frame leaves a thin gap.

Postcard limits in the US, Japan and Taiwan

The same card can be a postcard in one country and a letter in another.

The 4 × 6 card shows the difference. At 10.16 × 15.24 cm it fits the US postcard range and Japan’s privately made postcard range (up to 15.4 cm long), but in Taiwan its 15.24 cm long side exceeds Chunghwa Post’s 14.8 cm limit, so it may be charged as a letter there. That is why most postcards and free promotional cards printed in Taiwan are A6 (10.5 × 14.8 cm), the exact Taiwanese maximum.

Japan’s own pre-stamped postcards, called hagaki, are 100 × 148 mm (Article 21 of Japan Post’s terms), slightly narrower than A6. Source: Japan Post Domestic Postal Terms (PDF, Japanese).

Can I mail a photo print as a postcard?

Sometimes. In the US, a 4 × 6 photo print is within the postcard size range, but it must also meet the thickness limit of 0.016 inch and have room for the address and postage on the back. In Japan, a 4 × 6 print fits the size range but must also weigh 2–6 g and have a white or light-colored address side. A smaller 3.5 × 5 print is fine in the US but too small in Japan, where the minimum is 9 × 14 cm.

If you want to turn a phone photo into a 4 × 6 postcard:

1. Crop the photo to 2:3 first. Most phones shoot 4:3, and an uncropped 4:3 image will be trimmed automatically by the printer.
2. Check that the cropped photo has at least 1,200 × 1,800 pixels. A typical 4,032 × 3,024 phone photo cropped to 3:2 is 4,032 × 2,688, far more than needed, but images sent through messaging apps may be compressed, so print from the original file.
3. Print at a photo lab, a self-service kiosk, or at home on 4 × 6 photo paper with borderless printing.

How to address a postcard or letter to Taiwan

USPS’s country conditions for Taiwan say addresses “must be complete and written when possible in Chinese characters in addition to English.” Writing both is the surest way to get mail delivered; if you only have the English address, write the country line clearly in capitals. Source: USPS International Mail Manual, Taiwan, checked October 18, 2026.

English addresses in Taiwan run from the smallest unit to the largest, ending with the country. This is the sample Chunghwa Post (Taiwan’s postal service) shows in its international envelope guide, using its own headquarters:

Chunghwa Post Co., Ltd.
55, Sec. 2, Jinshan S. Rd.
Da'an District, Taipei City 106409
Taiwan (R.O.C.)

The same address in Chinese is written from the largest unit down, with the postal code first: 106409 臺北市大安區金山南路二段55號.

Taiwanese addresses use a few units that rarely appear in American addresses:

Taiwan’s postal codes have six digits (3 + 3): the first three identify the district (100 is Zhongzheng District and 106 is Da’an District in Taipei) and the last three narrow down the delivery area. If your contact only gives you three digits, the mail still arrives; six digits speed up sorting. If you have a Chinese address and need the English version, Chunghwa Post’s official Chinese address to English tool converts it.

The size limits earlier on this page are for domestic postcard pricing in each country; for international mail, check the sending country’s international postcard rules.

Is the postcard ratio 3:5 or 5:8?

Neither. A 4 × 6 card is 2:3 (long side ÷ short side = 1.5), and A6 is about 1:1.41. The ratios 3:5 (1.67) and 5:8 (1.6) are whole-number approximations of the golden ratio, which appear in math problems and design lessons but are narrower than real postcards.

Frequently asked questions

What is the standard postcard size in inches?

4 × 6 inches. The USPS postcard range runs from 3.5 × 5 to 4.25 × 6 inches.

What is the maximum postcard size for USPS?

4.25 × 6 inches and 0.016 inch thick. Larger cards are mailed as letters.

Is a 5 × 7 card a postcard?

Not for USPS pricing. At 5 × 7 inches it exceeds the 4.25 × 6 inch maximum and is mailed as a letter.

What size is a postcard in centimeters?

A 4 × 6 postcard is about 10.2 × 15.2 cm. An A6 postcard is 10.5 × 14.8 cm, and Japan’s hagaki is 10 × 14.8 cm.

How many pixels does a 4 × 6 postcard need?

1,200 × 1,800 pixels at 300 DPI. Add bleed of about 3 mm per side if your printer asks for it.

How do I write a Taiwan address in English?

Start with the floor and building number and end with the country, for example “55, Sec. 2, Jinshan S. Rd., Da’an District, Taipei City 106409, Taiwan (R.O.C.)”. USPS asks for the Chinese address as well when possible.

Is A6 bigger than 4 × 6?

They have almost the same area. A6 is slightly wider (10.5 cm vs 10.16 cm) and slightly shorter (14.8 cm vs 15.24 cm).