PDF Page Sizes: A4, Letter, Legal and More
Every page in a PDF has a defined size, and unlike a web page that flows to fit your screen, that size is fixed and absolute. It is baked into the file in real-world units. Understanding how those units work — and why an A4 page from a German colleague looks slightly different from the US Letter page your printer expects — saves a lot of confusion when documents print wrong, get cropped, or refuse to line up.
Page geometry is measured in points
PDF does not measure pages in pixels or millimetres. It measures them in points, where 1 point = 1/72 of an inch. This is the typographic point inherited from PostScript, and it never changes regardless of zoom level or screen resolution.
To get a page dimension, take the physical size and multiply by 72 per inch (or by 72/25.4 ≈ 2.835 per millimetre):
- A4 (210 × 297 mm) → roughly 595 × 842 points
- US Letter (8.5 × 11 in) → exactly 612 × 792 points
- US Legal (8.5 × 14 in) → exactly 612 × 1008 points
- Tabloid / Ledger (11 × 17 in) → exactly 792 × 1224 points
- A3 (297 × 420 mm) → roughly 842 × 1191 points
A page is landscape simply when its width value exceeds its height — there is no separate orientation flag; the numbers decide it.
ISO 216 (A-series) vs North American sizes
These are two different standards that rarely match exactly.
The ISO 216 A-series (A0, A1, A2 … A4, A5) is used almost everywhere outside North America. Its defining trick is the aspect ratio of 1:√2 (about 1.414). Halving any A-size along its long edge gives the next size down with the same proportions — fold A4 in half and you get two A5 sheets. A0 is defined as one square metre of area, and each step halves it. This is why a printer can scale A4 down to A5 with no awkward cropping or white borders.
North American sizes — Letter, Legal, Tabloid — are based on inches and do not share a constant ratio. Letter is 8.5 × 11; Legal keeps the same width but stretches to 14 inches. Because A4 is narrower and taller than Letter, a document designed for one will shift content or shrink slightly when forced onto the other. If a US recipient prints your A4 file "actual size," the margins move; "fit to page" rescales everything. Neither is wrong — they are just different paper.
MediaBox vs CropBox
Internally, a PDF page can carry several "boxes," but two matter most:
- MediaBox is the full physical sheet — the total size of the medium the page is meant to be printed on. Every page must have one. This is the size you usually mean by "the page size."
- CropBox is the visible/printable region, a rectangle inside (or equal to) the MediaBox. Viewers display and print the CropBox. If absent, it defaults to the MediaBox.
The distinction matters because cropping a PDF often does not shrink the actual sheet — it narrows the CropBox while the MediaBox stays the same, so the hidden content is still there, just clipped from view. That is exactly how the crop tool works: it sets a smaller CropBox per page rather than discarding data, which is non-destructive and reversible. Resizing, by contrast, rescales the page content to a genuinely different MediaBox dimension.
Setting or changing page size
- Starting fresh: pick a target size when you create a PDF, so A4 or Letter is correct from the first page.
- Converting between standards or normalising mixed pages to one consistent size: resize the PDF to rescale page geometry.
- Trimming visible margins or whitespace without altering the underlying sheet: use crop, which adjusts the CropBox only.
A practical tip: if a file mixes A4 and Letter pages and prints inconsistently, resizing every page to a single target is usually cleaner than cropping, because cropping leaves each page's true MediaBox untouched.
Related tools
To set, scale, or trim page dimensions, use Create PDF, Resize PDF, and Crop PDF.