Change PDF page size to A4, Letter or a custom format
Changing a PDF page size sets each page's media box to the target dimensions — A4, Letter or custom — and applies a matching transformation so the content scales proportionally onto the new page. The conversion runs locally in your browser; nothing is uploaded and text stays vector-sharp. Use it to standardize mixed-size documents, fix US Letter files for A4 printers, or meet a submission requirement that demands one exact page format.
How it works: a new media box plus one scaling matrix
Every PDF page declares its physical size through the media box — a rectangle in points, the unit the format inherited from PostScript at 72 to the inch. A4 is 595.28 × 841.89 points; US Letter is 612 × 792. Resizing a page has two parts, and both matter: the media box must be set to the target rectangle, and the existing content must be mapped onto it. Changing the box alone would just crop or letterbox the drawing at its old size.
This tool computes, per page, the ratio between target and source dimensions and takes the smaller of the width and height ratios as the uniform scale factor, so content always fits without distortion — the same rule as “scale to fit” in a print dialog. It then prepends a coordinate-transformation instruction (the cm operator with a matrix like 0.9724 0 0 0.9724 0 ty for Letter→A4) to the page’s content stream and writes the new media box. Prepending matters: PDF drawing operators execute in sequence, so a transform placed first re-maps everything that follows, including text placement and image drawing.
Because the aspect ratios of Letter (1:1.294) and A4 (1:1.414) differ, a fitted conversion in either direction leaves small margins on one axis rather than stretching the content — stretching would visibly distort every glyph. All of this happens in vector space: no page is rasterized, fonts remain embedded and selectable, and images keep their exact pixel data, now simply painted at a marginally different physical size. File size is essentially unchanged since only a few dozen bytes of transform and geometry are added per page.
Worked example: standardizing a mixed Letter/A4 filing
A 45-page court filing assembled from three sources: 30 pages of US Letter (612×792 pt) pleadings, 12 pages of A4 (595×842 pt) correspondence, and 3 odd 8.27×13 in scanner pages. The court requires uniform A4. Selecting A4 as the target resizes all 45 pages: for the Letter pages the width ratio 595/612 ≈ 0.972 binds (the height ratio 842/792 ≈ 1.063 would overflow the width), so their content shrinks 2.8% with about 72 points of extra height distributed as top and bottom margin; the A4 pages pass through at scale 1.0 untouched; the long scanner pages scale by 0.896 to fit their height. Input 9.8 MB, output 9.8 MB, processing under two seconds — and the file now feeds through a duplex printer without the tray-switching and auto-shrink artifacts mixed sizes cause.
Changing PDF page size — frequently asked questions
How do I convert a Letter PDF to A4 without cutting content off?
Scale-to-fit uses the smaller of the width and height ratios, so the whole page always fits inside A4. Letter is wider and shorter than A4, so the fitted content ends up about 3 percent smaller with slim bands of extra space top and bottom.
Does resizing a PDF page make the text blurry?
No. The content is transformed mathematically in vector space, not re-rendered to pixels, so text and line art remain sharp at any zoom. Embedded photos keep their original pixels, which are simply displayed at a slightly different physical size.
What unit does PDF use for page size?
PDF measures pages in points, where 72 points equal one inch. A4 is 595 x 842 points, US Letter is 612 x 792 points, and a custom size entered in millimeters is converted at about 2.835 points per millimeter.
Will the printed font size change after resizing to A4?
Yes, in proportion to the scale factor. Going from Letter to A4 shrinks content by roughly 3 percent, so 12 pt type prints at about 11.6 pt, which is rarely noticeable. Large size changes, like A5 to A4, change print size accordingly.
Can I make every page the same size in a mixed-size PDF?
Yes, and it is one of the main uses of this tool. Each page is scaled to the single target size independently, so a file mixing A4 pages with odd scanner sizes comes out uniform and prints cleanly.