Paper and Photo Size Chart: A, B and C Series, 4R/5R Photo Sizes, ID Photos and Instant Film in One Table

Size questions get confusing not because the numbers are hard to remember, but because “size” is not one system. A4 comes from an ISO international standard, a 4 × 6 photo comes from inch-based photo printing, Taiwan’s “1-inch” ID photo is a legacy name, postcard size in Taiwan is set by postal regulations, and instant film is decided by the camera maker. Put all five in one question (“which is bigger?”) and the answer gets messy.

Joe sorted every size topic on this site by which system the size comes from, and ended up with nine systems. Sizes inside one system can be compared directly; sizes across systems need to be converted to centimeters first. Each system is listed in full, so this page works as a single size chart.

System 1: ISO A series (international paper standard)

The A series has one rule: fold the long side in half and you get the next size. A0 folded gives A1, A1 folded gives A2, all the way to A10, and every size keeps the same 1 : √2 aspect ratio, so enlarging or reducing on a copier never distorts the page. That is why A4 to A3 is simply “enlarge”. There are larger sizes too: 2A0 is 118.9 × 168.2 cm and 4A0 is 168.2 × 237.8 cm, but those are for engineering drawings and large-format output.

In Taiwan, convenience-store printing offers only two ordinary paper sizes, A4 and A3; the official black-and-white and colour prices at 7-Eleven, FamilyMart, Hi-Life and OK are compared in Convenience-store printing prices.

System 2: ISO and JIS B series (same names, two sets of numbers)

The trap with B sizes is that there are two standards. ISO B and the Japanese Industrial Standard (JIS) B use different numbers, with every JIS size slightly larger, and Taiwan’s printing industry and Japanese stationery mostly follow JIS. Before giving someone a B5 size, confirm which standard you mean, or the few millimeters of difference will cause trouble at the binding stage. Relative to the A series, the sizes interleave: A6 is smaller than ISO B6, ISO B6 is smaller than JIS B6, and JIS B6 is smaller than A5.

System 3: ISO C series (envelopes that fit A-series paper)

The C series logic is simple: each envelope fits the A sheet with the same number, so choosing an envelope means choosing how many times to fold your A4. In practice you can only buy C4 to C6 plus DL; C0 to C3 exist on paper but at that size they are poster mailers rather than envelopes. In Taiwan, note that C4’s long side of 32.4 cm exceeds Chunghwa Post’s 23.5 cm limit for standard envelopes, so it is charged differently from an ordinary letter.

System 4: Inch-based photo sizes (2R to 20R)

Taiwanese photo names are where people go wrong most often: a “6-inch photo” is not 6 inches square; its long side is 6 inches. Multiply the 4 × 6 long side of 6 inches by 2.54 and you get 15.24 cm; the short side of 4 inches is 10.16 cm. Internationally there is also the R naming, common on printing-kiosk menus, where the number before R is the short side in inches; only 2R and 3R are rounded because their short sides have decimals. 10R and above are enlargements and framing sizes that photo labs quote separately. The full 4 × 6 guide is here: 4 × 6 photo size in cm.

The Japanese column needs attention because Japan’s default differs from Taiwan’s. Taiwan’s mainstream print is 4 × 6, while Japan’s is L-size (3R, 8.89 × 12.7 cm), one size smaller, and Japanese albums and frames are built around L-size. To get the 4 × 6 size in Japan, choose KG-size on the menu, not the default.

“5-inch” is the name in this table most likely to cause a mismatch. By the long-side rule, a 5-inch photo is 3R: 3.5 × 5 inches, 8.89 × 12.7 cm. The rule has no exception; the problem is that this size has nearly disappeared in Taiwan. Printing now starts at 4 × 6, many shops do not offer 3R at all, and staff may interpret “5-inch” as something else. No official standard governs shop names, so give the size in centimeters, or say 3.5 × 5 or 5 × 7, which cannot be misread.

Where to print a 4 × 6 — what online services, convenience-store kiosks and cross-border printing from Japan cost per print, how many you must order and what shipping costs — is compared in Photo Printing in Taiwan.

System 5: Taiwan’s ID photo “inch” (not an inch)

This system has the most misleading names. The “inch” in Taiwanese ID photos is a legacy name with no conversion to real inches: a 1-inch ID photo’s long side is 3.5 cm, which is 1.38 inches, not 1 inch. Multiplying ID-photo “inches” by 2.54 always gives the wrong number. Every country’s visa has its own rules, and they change, so check the receiving authority’s latest notice before applying. Details: Taiwan 2-inch ID photo size and graduation-gown ID photos.

System 6: Sizes set by regulations and authorities

This is the only system where the size comes from a rule rather than a paper standard, so its logic differs from the others. B6, A5 and 5 × 7 all look like postcards, but once they exceed Chunghwa Post’s maximum they are charged as letters. Before making a card, decide whether it will be mailed as a postcard; that matters more than whether it looks like one. Postage rules change, so check the post office before mailing. For postcard limits in the US, Japan and Taiwan side by side, see the Postcard Size Guide.

The mobile barcode belongs here for the same reason: its 6 × 2 cm is not a printing convention but a requirement in the e-invoice platform’s notes, which also specify the text under the barcode and its font size. See how to print a mobile barcode. With these sizes, only the official spec counts.

System 7: Device and object sizes (set by manufacturers)

What these share is that the maker or the machine decides the size, and users cannot change it, so the useful question is “which models and formats exist?” rather than “how do I convert it?” Instant film sizes are covered in Polaroid and Instax photo sizes, and booth strips in photo booth strip sizes. Photo frames are a different trap: the listed size is the photo it holds, the inner opening, and the frame itself is larger, so measuring the wrong thing means the photo will not fit. Laminating pouches are the reverse trap: they are always larger than the paper, because the edges need room to seal, so an A4 pouch does not measure exactly 21 × 29.7 cm.

The last three rows deserve a note: calendars and certificates are often asked about as if they had a standard size, but they do not. There is no national or international standard; each printer and stationery maker sets its own template, and certificates usually borrow A4 or 8-kai paper. Any number you find online is one maker’s choice, not a rule.

System 8: Conversion layer (pixels and Taiwanese paper “kai”)

The conversion layer is not about how big something is, but about how sizes translate, so it sits above all the systems. Pixels map physical size to a digital file and decide how large a design file must be to print sharply. The kai system is Taiwan’s printing industry’s own third paper language, which does not line up with either the A or B series, so confirm it separately with your printer.

System 9: ISO RA and SRA print sheets (one size larger than the finished page)

Printers do not print A4 on paper that is exactly A4. Full-bleed printing means printing beyond the finished edge and trimming, and the edge the press grips cannot be printed, so they need a raw sheet one size larger. That is what RA and SRA are for: RA is Raw format A, SRA is Supplementary Raw format A, with more margin. The one you will meet most is SRA3 (32 × 45 cm), a size larger than A3 (29.7 × 42 cm) and the main sheet for digital presses. When a quote says SRA3 rather than A3, that is what it means.

Three meanings of “inch” that do not convert

This table is where size questions go wrong most often. The same “7-inch” means a diameter for a cake, a long side for a photo, and is not an inch at all for an ID photo. When someone asks “how many inches”, first confirm what kind of object it is, then look up the matching system.

Which is bigger? Common side-by-side questions

Within one series, comparison is simple: the higher the number, the smaller the sheet, and each step is one fold. Across series, convert to centimeters first, because the A and B numbering systems are independent; that is why “A4 or B5, which is bigger?” gets asked so often. Photos and paper need the most care: A6 and 4 × 6 differ by only a few millimeters but belong to two systems with different ratios, so a 4 × 6 photo in an A6 frame leaves a thin gap.

Frequently asked questions

Why split sizes into separate systems?

Because each size comes from a different source: the A, B and C series come from ISO standards, photo inches come from imperial photo printing, Taiwan’s ID-photo inches are a legacy name, postcard sizes come from postal regulations, and instant film and photo booth formats come from the manufacturers. Sizes inside one system can be compared directly; across systems, convert to centimeters first.

Which is bigger, A4 or B5?

A4 (21 × 29.7 cm) is bigger than JIS B5 (18.2 × 25.7 cm). The A and B series are independent and their sizes interleave; B5 sits between A5 and A4.

Is a 7-inch photo 17.78 cm square?

No. A photo’s “inch” refers only to the long side. A 7-inch photo is 12.7 × 17.78 cm; only the long side is 7 inches.

Is a 1-inch ID photo 2.54 cm?

No. In Taiwan the ID photo “inch” is a legacy name unrelated to real inches. A 1-inch ID photo is 2.8 × 3.5 cm, and its 3.5 cm long side is 1.38 inches.

Which envelope fits A4?

It depends on how many times you fold it: C4 (22.9 × 32.4 cm) unfolded, C5 (16.2 × 22.9) folded once, C6 (11.4 × 16.2) folded twice, and DL (11 × 22) folded in three.

What size is a “5-inch photo”?

By the rule it is 3R, 8.89 × 12.7 cm, because a photo’s inch figure is its long side. But this size has nearly disappeared in Taiwan and many shops do not offer it, so state centimeters or say 3.5 × 5 or 5 × 7 when ordering.

What is the difference between SRA3 and A3?

SRA3 is 32 × 45 cm and A3 is 29.7 × 42 cm. SRA sheets are raw printing paper; the extra margin is for bleed and the press grippers and is trimmed off. A quote that says SRA3 refers to the sheet going into the press, not the finished size.

Is there a standard size for certificates or calendars?

No. There is no national or international standard; each printer sets its own template, and certificates usually borrow A4 or 8-kai paper.

Can a postcard be A5 in Taiwan?

You can print one, but it will not travel at the postcard rate. Chunghwa Post’s postcard maximum is 14.8 × 10.5 cm, A5 (14.8 × 21 cm) exceeds it, and it will be charged as a letter.