A printable paper size chart covering A series B series and US letter formats

The A series and the math behind it

The ISO 216 A series rests on a single mathematical insight. A rectangle whose long side equals the short side multiplied by the square root of two has the property that folding it in half along the long side produces another rectangle with the same proportions. The German engineer Walter Porstmann formalized this in 1922 and it became the basis for the international paper size standard that almost every country except the United States and Canada now uses.

The base size A0 measures one square meter. Specifically 841 by 1189 millimeters, with the dimensions chosen so that the area is exactly one square meter and the ratio of long to short side equals the square root of two, approximately 1.4142. Each subsequent size in the A series is half the area of the previous size. A1 is half of A0. A2 is half of A1. A4, the everyday office size, is one sixteenth of A0 at 210 by 297 millimeters. The mathematical elegance of the system extends to the everyday: a folded A4 brochure becomes A5 sized, and printing A5 spread across the long side of A4 produces an A4 booklet. The everyday distinction between an MFP that handles A3 and one that handles only A4 is part of the broader segment classification covered at What the industry copier segments from one through six actually mean for you.

The B series for sizes between A sizes

The ISO 216 B series complements the A series. B sizes sit between adjacent A sizes. B5 falls between A5 and A4. B4 between A4 and A3. The geometric relationship is that each B size has a long edge equal to the short edge of the corresponding A size multiplied by the square root of two. The result is a series of intermediate sizes for applications where the A series gap is too wide.

Practical use of the B series varies by industry. Japanese textbook publishing uses B5 as the standard book size, between European A5 paperback and American 6 by 9 inch trade paperback dimensions. Some envelope makers use B series sizes to fit A series content without folding. Concert posters in Europe sometimes use B2 or B1 when an A2 or A1 would be too small but the next A size up would exceed the printer capacity.

Office MFPs typically support B4 and B5 in their paper tray configurations, though both sizes are uncommon in everyday Spanish office work. The user might encounter B5 when handling Japanese trade documents or B4 when printing certain technical drawings. Setting the tray to B size paper requires a configuration change on the panel, since the default tray detection assumes A series. Where the relationship between paper handling complexity and segment class shows up is at What the industry copier segments from one through six actually mean for you.

The North American sizes

The United States and Canada use a different system. Letter, Legal, and Tabloid are the three primary sizes, with several less common variants. The dimensions trace back to nineteenth century printing tradition and remain in use today through industry inertia despite the international move to ISO 216. Letter measures 8.5 by 11 inches, or 216 by 279 millimeters, almost the same size as A4 but not exactly. Legal measures 8.5 by 14 inches. Tabloid measures 11 by 17 inches.

The minor dimension difference between A4 and Letter creates regular problems for documents crossing the Atlantic. A Letter formatted document printed on A4 paper produces extra blank space at the bottom of each page. An A4 formatted document printed on Letter paper either crops the bottom edge or scales down the entire page to fit, depending on the driver setting. Most modern drivers default to scale to fit and handle the conversion automatically, but the conversion can shift line breaks, margin alignment, and page totals on long documents. The deeper read on what the controller does at the rasterization stage to handle these conversions sits in the foundational mechanics at How a photocopier actually works in six clear steps.

For Spanish offices that do business with American clients, configuring the print server with both A4 and Letter as available paper sizes, and setting the document size to match the source format rather than always defaulting to A4, prevents the auto scale shifts. The setting takes a minute on the print server and applies to every document going through the queue. The everyday distinction between MFPs that handle these conversions transparently and ones that need explicit user action shows up most clearly in the controller and software stack characteristics at The simplest possible explanation of what a multifunction printer does.

Paper weight and how it intersects with size

Paper weight, measured in grams per square meter (gsm) in Europe or pounds per ream in the United States, varies independently of paper size. Standard office paper runs 80 gsm in Europe, equivalent to 20 pound bond in the US. Heavier paper for cover stock, presentations, and certain marketing materials runs 100 to 200 gsm. Card stock for business cards and tickets runs 250 to 350 gsm.

An MFP fuser has a maximum paper weight rating beyond which the toner does not bond reliably. Office class machines typically handle up to 250 to 300 gsm through the bypass tray, with the regular paper trays limited to 105 to 200 gsm depending on segment. Production class machines extend the bypass capability to 350 gsm or higher, with some models supporting up to 400 gsm for specialty card stock. Pushing paper above the rated weight risks paper jams in the fuser, toner adhesion failures, and in extreme cases damage to the fuser rollers. The deeper context for fuser limitations and where they sit in the broader chassis architecture is at A guided tour of every part inside a modern office copier.

The intersection of paper size and weight matters most when planning specific projects. A small business printing wedding invitations might want to produce A6 cards on 250 gsm card stock, which works on most Segment 3 office MFPs through the bypass tray but fails on Segment 1 desktop units that cap at 200 gsm. A real estate firm printing color brochures on 150 gsm coated paper at A4 size works on any Segment 2 machine and above. Knowing both numbers, size and weight, before sending the job to the printer prevents the most common cause of bypass tray jams.

How to read a paper size from a print dialog

A typical print dialog on Windows or macOS shows a paper size dropdown with regional defaults at the top. In Spain, A4 appears first, followed by A5, A3, Letter, Legal, and a long list of less common sizes. Selecting the correct size for the job ensures the printer produces output at the requested dimensions rather than relying on the printer default.

The catch. The driver paper size setting must match the paper actually loaded in the tray for the printer to behave correctly. If the driver requests A4 but the tray contains Letter paper, the printer either prompts the user to confirm the paper mismatch on the panel, prints anyway with cropping, or rejects the job entirely depending on the chassis configuration. Most office IT teams set the trays to the office regional default and configure the print server to match, eliminating the mismatch as a recurring problem.

For shared multi tray machines, individual trays can hold different sizes simultaneously. Tray 1 with A4. Tray 2 with A3. Tray 3 with Letter. Bypass tray with whatever the current job needs. The driver pulls from the appropriate tray based on the requested paper size, automatically routing the job to the correct stock. This setup matters most for offices that handle multi region documents regularly or that produce occasional A3 work alongside daily A4 output. The detailed mechanical view of paper trays and how they integrate with the chassis paper path is at A guided tour of every part inside a modern office copier.