Resize PDF to Letter Size converts every page of a document to US Letter, 8.5 by 11 inches, which a PDF stores as 612 by 792 points. The usual reason is an A4 file that has to be printed or submitted in the United States or Canada. A4 is 210 by 297 mm, about 6 mm narrower and 18 mm taller than Letter, so a printer loaded with Letter paper either cuts off the footer or shrinks each page by its own rule, and an upload portal that checks page dimensions may reject the file outright. Converting the PDF itself removes the guesswork. With Fit to size, an A4 page is scaled to about 94% so its full height fits on Letter, and the spare width becomes a narrow white margin on the left and right. Text stays sharp, because PDF content is scaled as vectors rather than turned into an image. With Add white space, pages already smaller than Letter keep their exact printed size and are centred, which matters for forms and drawings, while larger pages are still reduced so nothing falls off the edge. Landscape pages can become Letter landscape, 11 by 8.5 inches, so wide tables stay readable. The tool also measures the file first and lists which pages are not Letter yet, so a mixed document from several sources is fixed in the same pass. Everything runs in your browser and the PDF is never uploaded. For the opposite direction use Resize All PDF Pages to A4, to trim white margins instead of changing the format use PDF Crop & Resize, and to combine several files before converting them use PDF Merger.
The reason inconsistent page sizes are so annoying is that nothing warns you about them. A PDF viewer happily renders a file where page 4 is Letter and the rest are A4, and the difference is only 6 mm wider and 13 mm shorter, which is invisible on screen. The cost arrives at the end of the process: a print driver set to "actual size" produces pages with different margins, a duplex job feeds wrongly, a submission portal that validates page dimensions rejects the upload, or a reader sees the page jump as it scrolls. Most PDF services offer resize, crop and compress as separate operations and leave the diagnosis to the user, which is the hard part. This tool inverts that order. It measures first, tells you in plain language what it found, and offers one button that applies the obvious fix. Only if you want something else do the other options matter. A few practical notes. Scanned pages rarely match a standard format to the decimal, so sizes within roughly 0.7 mm of each other are treated as the same format rather than reported as separate groups; this keeps the summary honest instead of listing twenty near-identical sizes. Pages carrying a rotation flag are measured as the reader sees them, so a portrait page rotated 90 degrees is correctly grouped with the landscape pages. The output is a standard PDF that opens in Acrobat, Preview, Chrome and any mobile reader, with text, fonts, links and images preserved. If your real problem is uneven white margins rather than uneven page sizes, PDF Crop & Resize is the better tool, since it trims the margins directly. If pages came from several source files, run PDF Merger first and normalise the combined document in one pass, and use PDF Page Count Checker to confirm the final file has every page you expect.