Is your PDF really A4, or is it US Letter? The two sizes look alike on screen, yet they print differently. The PDF Page Size Detector reads every page and reports its exact width and height.
It is made for designers, print shop staff, and office teams who must check a file before printing or sharing. You upload one PDF, and the tool fills a table with one row per page. It only reads the file. It never changes it.
Table of Contents
- What the PDF Page Size Detector Does
- How to Use It, Step by Step
- How It Works
- Privacy and File Handling
- Example: Checking a Mixed Contract
- How to Read the Results
- What to Do After You Find a Mismatch
- Limitations
- FAQs About the PDF Page Size Detector
What the PDF Page Size Detector Does
The tool measures each page and names the closest standard paper size. It also shows four summary cards above the table.
- Most Common Format: the paper name of the size most pages share. If sizes tie, the earliest page wins.
- Dimensions (mm): the width and height of that most common size, in whole millimeters.
- Dimensions (Inches): the same size, with one decimal.
- Mixed Page Sizes?: shows "Uniform Size" or "Yes (Multiple Sizes)".
- Show Sample Result fills the screen with a fixed demo. Copy Dimensions List copies the table rows as text.
How to Use It, Step by Step
- Drag a PDF onto the box that reads "Drag & drop PDF to detect page dimensions". You can also click the box and pick a file.
- Wait for the status line to say "Done." with the number of pages measured.
- Read the four cards at the top. They describe the most common page size.
- Scan the table. Its columns are Page #, Format Name, Width × Height (pt), Width × Height (mm), and Width × Height (Inches).
- Check "Mixed Page Sizes?" to see whether every page matches.
- Press "Copy Dimensions List" to copy the rows into a note or spreadsheet.
How It Works
The tool opens your PDF with the pdf-lib library and asks each page for its visible size. That is the crop box, or the page box if none is set. If a page is rotated 90 or 270 degrees, width and height swap.
Sizes come back in points. There are 72 points in one inch.
Upload PDF→Read Each Page Size→Convert to mm and Inches→Match a Paper Name
Millimeters use 0.352778 per point. For the name match, both sides are rounded to whole millimeters. A page matches a name when each side is within 5 mm of the standard size.
The tool knows six names: A4, US Letter, US Legal, A3, A5, and Tabloid / Ledger. It sorts the short and long sides first, so portrait and landscape pages get the same name. Anything else shows as Custom, followed by the short and long side in millimeters.
Privacy and File Handling
Your PDF is read inside your browser. The code loads the file into memory and measures it with pdf-lib. It does not send the file to any server.
The page does download the pdf-lib script from a public code host when it loads. That script does not carry your file. The tool keeps no copy, so you must upload the file again after a reload.
Example: Checking a Mixed Contract
Priya Nair builds a three page contract for a print shop. She drops the file on the tool. Pages 1 and 2 are letter pages, and page 3 is a longer legal exhibit.
| Page # | Format Name | Points | Millimeters | Inches |
|---|
| Page 1 | US Letter | 612.0 × 792.0 pt | 215.9 × 279.4 mm | 8.50" × 11.00" |
| Page 2 | US Letter | 612.0 × 792.0 pt | 215.9 × 279.4 mm | 8.50" × 11.00" |
| Page 3 | US Legal | 612.0 × 1008.0 pt | 215.9 × 355.6 mm | 8.50" × 14.00" |
The cards read US Letter, 216 × 279 mm, and 8.5" × 11.0". The last card reads Yes (Multiple Sizes). The status line says "Done. 3 pages measured." Priya will warn the printer about the longer page.
How to Read the Results
- Format Name is the closest match within 5 mm per side. It is not a promise that the file is exactly that size.
- Custom appears when no standard size fits. A label such as Custom (200x250 mm) lists the short side first.
- Millimeter values show one decimal in the table and whole numbers in the cards.
- Mixed Page Sizes? compares real sizes, with a 1 point allowance. A portrait page and a landscape page of one size count as mixed. So do pages that differ by more than 1 point, even if both get the same name.
- (rotated 90°) beside a Format Name marks a rotated page. The size shown matches what a viewer displays.
What to Do After You Find a Mismatch
This tool only reports sizes. To see more detail, the PDF page dimension viewer shows measurements in a different layout. The PDF orientation detector tells you which pages are portrait or landscape.
To fix a mismatch, use a tool that changes the file. The Convert PDF to A4 tool and the letter size converter set one target size. The resize PDF pages tool handles other targets. More options sit in the PDF tools hub.
Limitations
- The tool reports only. It cannot resize, crop, or fix a page.
- It handles one PDF at a time. If you drop several files, only the first is checked.
- Copy Dimensions List adds a header row. With no file loaded, it asks you to upload a PDF first.
- Show Sample Result does not load a real file. It always shows a three page A4 demo, and the page labels it as example data.
- The code asks pdf-lib to ignore encryption, so some locked files may still be measured. The page then warns that sizes "may be incomplete".
- A damaged file shows "This PDF could not be read." A file with no pages shows "This PDF has no pages to measure."
FAQs About the PDF Page Size Detector
Does the PDF Page Size Detector upload my file?
No. The code reads the file in your browser and sends it nowhere.
Which paper sizes can the tool name?
It names A4, US Letter, US Legal, A3, A5, and Tabloid / Ledger. Every other size shows as Custom with its millimeter values.
Why do the cards show only one size for a long file?
The cards describe the most common size. The table below them lists every page, and the last card flags mixed sizes.
What does Custom mean in the Format Name column?
It means the page is more than 5 mm away from every standard size the tool knows. The label gives the rounded short and long sides.
Can this tool change my page size?
No. It only measures. Use a converter or resize tool to change the size, then check the new file here.
Why does Show Sample Result always show the same numbers?
The button does not read a file. It writes a fixed A4 example into the cards and table so you can see the layout.
This tool runs in your web browser and may not handle every PDF file, font, or browser the same way. Keep a backup of your original file. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.