Deskew PDF
Straighten crooked pages in a scanned or photographed PDF. Each page is measured, the angle is shown on its card, and you can change or skip any page. Text and drawings stay sharp and selectable, because the page content is turned, not redrawn as a picture.
- Files stay on your device. Nothing is uploaded.
- Free, no sign-up, no daily limit.
- Works with Wi-Fi off once the page has loaded. Check it yourself
Updated by Khokhar Sab
How do I deskew a PDF?
Press Choose a PDF. Every page is measured and shown as a card with the tilt found, and the picture already shows the page turned straight. Untick a page to leave it alone, or type a different angle. Press Straighten pages, look at the preview, then Download the straightened copy of your PDF.
- Press Choose a PDF and wait for the pages to be measured.
- Check each card; untick a page or type your own Tilt.
- Press Straighten pages.
- Check the preview, then press Download.
How do I straighten a scanned PDF?
Open the scan here. A scanned page is one picture, and the tool measures the lines of text in that picture, then turns the picture back by the same angle. Pages with no text, such as photos, are left as they are. After straightening, OCR PDF can read the text more accurately than on the tilted scan.
Straight lines matter for text recognition: the Tesseract project lists deskewing among the steps that improve its results. Run OCR PDF on the straightened file to make it searchable.
Does deskewing keep the text selectable?
Yes. Redrawing a page as a new image would turn real text into pixels and can blur it, so this tool adds one rotation instruction around the page's own drawing, so text, lines and pictures keep their quality. In our test file the size grew by 0.26%, and every character could still be copied.
| Test page | Real tilt | Tilt found | Tilt after | Text characters before / after |
|---|---|---|---|---|
| Text page with a link | 2.5° | 2.5° | 0.0° | 1055 / 1055 |
| Straight text page | 0.0° | 0.0° | 0.0° | 1055 / 1055 |
| Scanned page (picture) | 1.8° | 1.8° | 0.0° | none (a picture) |
| Text page shown turned (/Rotate 90) | minus 3.2° | minus 3.2° | 0.0° | 1055 / 1055 |
Whole file: 134 KB before, 134 KB after.
How does the tool measure the tilt?
It renders each page about 1,000 pixels wide and looks at the dark pixels. For each angle from minus 7 to 7 degrees it counts how many fall on the same slanted line; at the right angle the text lines line up and the count peaks. A first pass checks every half degree, a second every 0.05 degrees.
Will the corners of my page be cut off?
Only content right at the corners can move, because the page keeps its size and turns around its center. On a Letter page a corner moves about 8.7 points per degree, so a 2 degree turn shifts it about a quarter of an inch. Pages with normal margins lose nothing. The table uses the tool's own matrix.
| Turn | Top-left corner of a Letter page moves |
|---|---|
| 1° | 8.7 points (3.1 mm) |
| 2° | 17.5 points (6.2 mm) |
| 3° | 26.2 points (9.2 mm) |
| 5° | 43.7 points (15.4 mm) |
Should I deskew or rotate a PDF?
Rotate when a page is sideways or upside down: that needs a quarter or half turn, which Rotate PDF saves as the page's display angle. Deskew when a page is slightly crooked, by a few degrees, so the lines of text slope. A sideways scan that is also crooked needs both, rotating first.
For quarter turns, use Rotate PDF, then come back to straighten the small tilt.
Limits and fixes
- Pages without text, such as photos or drawings, usually measure as straight; type the angle by hand.
- Tilts over 7 degrees are not found on their own; type them in, up to 20 degrees.
- Links and comments move with the text, but their boxes stay upright.
- Locked PDFs need their password removed first with Unlock PDF.
- Digital signatures stop being valid, because the pages change.
Frequently asked questions
Is it free?
Yes, with no sign-up and no page limit.
Is my PDF uploaded?
No. Pages are measured and turned in your browser.
Does it work on PDFs made from phone photos?
Yes, for tilt. For pages photographed at a slant, with a wider top than bottom, use Scan to PDF, which flattens the page.
Can I straighten only some pages?
Yes. Untick the pages to leave alone; they are copied as they are.
Does it lower the quality of a scan?
No. The picture inside the page is not recompressed; it is shown turned.
Related PDF tools
How this tool was built and tested
- ISO 32000-1 (PDF 1.7), sections 8.3.4 Transformation matrices and 8.4.4 Graphics state operators: the cm operator that turns the page content
- Tesseract documentation: Improving the quality of the output: why straight lines matter for OCR
- J. J. Hull, "Document Image Skew Detection: Survey and Annotated Bibliography" (1998): the projection-profile method used to measure the tilt
- PDF.js (Apache-2.0): renders the pages for measuring and the previews
- pdf-lib, Cantoo fork (MIT), version 2.11.1: writes the turned pages