PDF page sizes explained: A4, Letter, points and DPI
How PDF measures pages, the dimensions of common paper sizes, and how to avoid printing problems when documents cross the Atlantic.
By the PDF365 editorial teamUpdated 6 min read
Every page in a PDF has a fixed size. Most of the time you never think about it, until a footer gets clipped at the printer or a form comes out tiny in the middle of the sheet. Once you know how PDFs measure pages, those problems are quick to sort out.
PDF measures in points
Inside a PDF, sizes are given in points. One point is 1/72 of an inch, or about 0.353 mm. So a page that’s 595 points wide is 595 ÷ 72 = 8.27 inches, or 210 mm: the width of A4. Points are just a unit of length. They tell you nothing about screen pixels or image resolution.
Common paper sizes
| Size | Millimetres | Inches | Points |
|---|---|---|---|
| A3 | 297 × 420 | 11.7 × 16.5 | 842 × 1191 |
| A4 | 210 × 297 | 8.27 × 11.69 | 595 × 842 |
| A5 | 148 × 210 | 5.83 × 8.27 | 420 × 595 |
| US Letter | 216 × 279 | 8.5 × 11 | 612 × 792 |
| US Legal | 216 × 356 | 8.5 × 14 | 612 × 1008 |
The A sizes come from the international ISO 216 standard. Each size is half of the one above, and every A size has the same proportions (a ratio of 1 to the square root of 2), so an A3 poster scales down to A4 without distortion. The US and Canada use Letter and Legal instead, which have a different, slightly squarer shape.
Why Letter documents print badly on A4 (and vice versa)
Letter is 6 mm wider than A4 but 18 mm shorter. Print a Letter PDF on A4 paper at actual size and you get extra white space at the bottom and slightly clipped sides. Print an A4 document on Letter paper and the bottom of the page, often the footer or page number, can be cut off. Printing with “Fit to page” avoids clipping but shrinks everything a little.
If a document’s going to be printed on the other side of the Atlantic, it’s kinder to convert it once yourself than to make everyone fiddle with printer settings. Resize Pages scales each page to the new paper and centres it, so nothing is cut off.
Pixels and DPI
Images inside a PDF have pixel dimensions, and how sharp they look depends on how many pixels are squeezed into each inch of the page: the DPI (dots per inch). A 1,200-pixel-wide photo stretched across an A4 page (8.27 inches) gives about 145 DPI, which looks fine on screen and acceptable in print. Commercial printers usually ask for 300 DPI.
When converting pages to images with PDF to JPG, you choose the DPI. An A4 page at 150 DPI becomes about 1,240 × 1,754 pixels; at 300 DPI, about 2,480 × 3,508 pixels.
Page boxes: why “size” isn’t always one number
PDF pages can define several boxes. The media box is the full sheet. The crop box is the area viewers display and printers print; it’s what changes when you crop a PDF. Professional printers also use trim and bleed boxes to mark where paper will be cut. Most of the time only the first two matter.
Rotation
A landscape page might be stored as a landscape-shaped page, or as a portrait page with a rotation setting of 90 degrees. You can’t tell the difference in a viewer. That’s also why rotating PDF pages doesn’t cost any quality: Rotate PDF simply changes the rotation setting.
One last practical note: most PDF software tops out at 200 × 200 inches per page, so if you’re making giant posters or plans, you’ll hit that limit before anything else.