A document written in the United States arrives on US Letter; one written almost anywhere else arrives on A4. They look identical on screen and differ just enough that printing one on the other clips a line or leaves a stripe of white down the side. Here is what page size really is inside a PDF, and how to change it with Resize PDF Pages.
Page size is a rectangle, not a resolution
Every page carries a rectangle called the MediaBox saying how big the sheet is, measured in points of 1/72 inch. It is the only thing deciding what size the page prints. A4 is 595 x 842 points; US Letter is 612 x 792. Letter is wider, A4 is taller, and neither fits inside the other - the root of every problem here.
A second rectangle, the CropBox, says how much of that sheet a reader actually displays. Most files leave it equal to the MediaBox, but scanned and press-ready documents crop in. The CropBox is what you see, so it is what a resize has to work from - otherwise trim marks and scanner edges you have never seen would reappear.
What is not in either rectangle is quality. Text is stored as instructions to draw glyphs at coordinates, not as pixels, so resizing re-draws it and it stays perfectly sharp. Photographs are the one exception, and even they only soften if you enlarge a page well past its original size.
Change the page size in four steps
- Open Resize PDF Pages and drop your PDF onto the box. It is read inside your browser tab, not uploaded.
- Pick the new page size. A4, US Letter, Legal, A3, A5, A6, B5, Executive and Tabloid are listed, and Custom size takes any width and height in millimetres or inches.
- Choose an orientation. Keep each page's is the safe default; Portrait and Landscape force every page the same way round.
- Leave Content on Fit to page unless you have reason not to, then click Resize and download. The line above the button says exactly what will happen first.
A worked example: Letter to A4
Take a US Letter page, 612 x 792 points, and convert it to A4 at 595 x 842. Fitting scales the content until the first edge touches, so it takes the smaller of the two ratios:
- Width ratio: 595.28 / 612 = 0.9727
- Height ratio: 841.89 / 792 = 1.0630
- Scale used: the smaller of the two, 0.9727 - shown in the tool as 97%
The content becomes 595 points wide, exactly filling the A4 width, and 770 points tall on a page 842 points tall. The 72 points left over are split evenly, so the content sits centred with about 12.7 mm of white above and below. Nothing is cut off and nothing is stretched, because the same factor is applied to width and height.
Going the other way, A4 to Letter, the height binds instead: 792 / 841.89 = 0.9407, or 94%, leaving about 9 mm of white down each side. That is the honest answer to "why is there a border on my converted PDF": the two shapes differ, and removing the border would mean cropping or distorting your content.
Fit to page, actual size, or scale by percentage
The Content setting decides how the existing page is mapped onto the new one, and picking the wrong one is the usual cause of a disappointing result.
- Fit to page scales the content so all of it lands inside the new page, keeping its proportions. This is what you want for almost every A4-to-Letter conversion.
- Keep actual size leaves the content at its original scale and changes only the sheet around it. Use it when physical size matters - a technical drawing, a music score. If the old page is larger, the edges are cut off, and the tool says so before you download.
- Scale by % applies a factor from 10% to 200%, for when the scaling itself is the goal - shrinking to 70% to fit two pages on one sheet.
Fit to page adds two controls. Margin keeps a band clear on all four sides, for printers that cannot reach the paper edge or for binding. Never enlarge stops a small page being blown up to fill a large one, so a receipt stays receipt-sized in the middle of an A4 sheet.
Mixed page sizes and rotated pages
Documents assembled from several sources are rarely uniform - a report might be A4 throughout except for two landscape A3 charts and a scanned receipt. Dropping the file in reports how many distinct sizes it holds, one preview line per size with the pages it covers, so you see what each group becomes before anything is written.
Orientation is what stops this going wrong. On Keep each page's, a landscape page becomes landscape A4 and a portrait page portrait A4 - one paper size, each page still the way round it was drawn. Force Portrait and those charts are turned upright: right for a uniform stack to bind, wrong if you need to read them.
Rotation deserves its own note, because a PDF can store a page one way round and display it another: a sideways scan is often stored portrait with a flag telling the reader to turn it. The resize works from what you see, not what is stored, and preserves the flag rather than baking it in.
Resizing is not compressing
This is the commonest mix-up, because "resize" means something different for images. Changing page size changes the sheet, not the data: the same text, fonts and images are still there, drawn at a different scale. Converting a 4 MB PDF from Letter to A4 gives you a 4 MB PDF.
A smaller file is a different job: Compress PDF reduces image quality, and Compress PDF to Size searches for the setting that lands the file under a limit you name - what you want when an upload form refuses anything over 2 MB. They compose: resize first, compress afterwards.
What survives the conversion
Many resize tools re-draw each page as one flattened graphic. That looks right and quietly destroys everything interactive: links stop working, form fields become pictures of form fields, bookmarks vanish. Resizing in place avoids that - links, form fields, comments and outlines are carried across, each moved and scaled by the same amount as the content so it still sits over what it points at.
Text stays selectable and searchable, because nothing is converted to an image at any point. To confirm it, resize a document with a link in it, then click the link in the result and select a sentence while you are there.
Nothing leaves your browser
The whole conversion runs on your own machine, in the page you have open, and no part of the document is sent anywhere - which matters, because the files most often needed on a specific paper size are contracts, application forms and scanned identity documents. You can check it the blunt way: load Resize PDF Pages, disconnect from the internet, and resize a file. It still works.
Frequently asked questions
- Does changing the page size reduce the quality of my PDF?
- No. Text and vector graphics are stored as drawing instructions rather than pixels, so they are simply re-drawn at the new size and stay perfectly sharp however much you scale them. Photographs inside the page keep their original pixels, so shrinking a page actually increases their effective resolution, and only a large enlargement - well past double - starts to look soft.
- Why does my Letter page get a white border when I convert it to A4?
- Because A4 and Letter are different shapes, not just different sizes. A4 is narrower and taller, so fitting Letter content into it scales until the width fits exactly and leaves roughly 12.7 mm spare split between the top and the bottom. The only ways to remove that band would be to crop your content or to stretch it out of proportion, and neither is what you want. Setting the margin to 0 keeps the band as small as the two paper shapes allow.
- Can I resize only some of the pages in a document?
- The tool applies your chosen size to every page, because the usual reason for resizing is to make a document uniform. If you genuinely need mixed sizes, split the file with Split PDF, resize the part that needs it, and merge the pieces back together with Merge PDF. If your worry is landscape pages being turned upright, you do not need to split anything - leave Orientation on "Keep each page's" and they stay landscape.