Deskew Scanned PDF
Detect crooked scanned pages and straighten each one automatically, or set the angle yourself.
Select a scanned PDFor drop it anywhere on this page, or paste
Opens in your browser. Nothing is uploaded.
Deskew Scanned PDF, free and private
Deskew a scanned PDF and each crooked page is turned back so its text runs level. Pages rarely go through a scanner square. A tilt of one or two degrees makes text lines run downhill and can lower OCR accuracy.
Auto deskew measures the tilt of each page on its own. You can also set one manual angle for the whole file. Pages are straightened in your browser, so a scanned contract or form is never uploaded.
How to straighten a scanned PDF
- 1
Add the scanned PDF
Press Select a scanned PDF or drop the file on the page.
- 2
Choose the correction
Under Correction, keep Automatic to detect the tilt of each page. Or pick Manual angle and set a clockwise angle from -15° to 15°, in steps of 0.1°. The preview shows each page turned, with level guide lines. If a page looks wrong, move the slider for that page to set its own angle.
- 3
Set the image quality
Move the Image quality slider between 65% and 95%. The default is 85%. Higher keeps more detail, lower makes a smaller file. Keep straight pages as they are is on by default, so pages that need no turn are copied unchanged.
- 4
Straighten and download
Press Straighten PDF. The summary shows how many pages were turned, how many straight pages were kept and the average correction. Press Preview to check, then Download straightened PDF.
Why use PDFToolz for this
Each page measured on its own
In Automatic mode, a stack of scans where each sheet went in at a different angle is fixed page by page.
Exact manual angle
If you know the angle, Manual angle turns every page by the same amount, up to 15° either way. If auto detection gets one page wrong, set that page's angle on the preview.
Page size kept
Each straightened page has the same size as the original, so the file prints the same way.
No upload
Rendering, detection and rebuilding all run on your device. That matters for scanned IDs, medical forms and signed paperwork.
What is auto deskew?
Auto deskew is automatic skew correction. Software works out how far a scanned page is tilted and turns it back by the same amount, with no angle typed in by you. Most methods look for the main direction of the text lines, since on a straight page they run level.
This tool uses a projection profile. It draws each page, makes a small copy and turns that copy through every angle from -5° to +5° in half-degree steps. At each angle it measures how sharply the amount of dark ink changes from one pixel row to the next. When text lines are level, rows switch cleanly between dark text and white gaps, so the score peaks. The best angle is then applied to the full page.
Since it relies on text lines, auto deskew works best on text-heavy pages tilted by less than 5°. Pages that are mostly photos, diagrams or white space may stay unchanged or get a small wrong correction. Use Manual angle for those.
Automatic or manual angle
Pick the mode that matches how the pages went wrong:
- Automatic: pages tilted by different amounts, mostly text, less than 5° off.
- Manual angle: every page tilted the same way, for example from a misaligned feeder, or a tilt between 5° and 15°, or a page auto mode got wrong.
- Direction: positive values turn clockwise. If text lines climb toward the right edge, try a positive angle. If they drop, try a negative one.
- Sideways or upside-down pages: use Rotate PDF. Deskew is for small tilts, not 90° or 180° turns.
What deskewing does to your PDF
To straighten a page, the tool has to rotate a picture of it. Each tilted page is drawn at 160 DPI, rotated on a white background and saved into a new PDF as a JPEG. That suits image-only scans. On those pages any existing text layer, links and form fields are lost. Pages that are already straight are copied unchanged unless you turn off Keep straight pages as they are.
A rotated page takes up a little more room, so the image is scaled down slightly to fit the original page size. The corners it leaves are filled white.
After straightening, trim uneven white edges with Crop PDF. If the file is large, use Compress PDF on Light, which keeps the most detail for text recognition. Run OCR PDF last to make the text searchable again, since compressing after OCR would drop the text layer.
Frequently asked questions
Auto deskew finds how far a scanned page is tilted and turns it straight for you. This tool tests each page at angles from -5° to +5° and applies the angle where the text lines line up best.
Add the PDF, keep Correction on Automatic and press Straighten PDF. It runs free in your browser and nothing is uploaded.
Automatic mode finds tilts of up to 5° either way, in half-degree steps. Manual angle takes any value from -15° to 15° in steps of 0.1°.
Not on the pages that were turned. They are rebuilt as images, so their text layer is lost. Pages that were already straight keep theirs. Run OCR PDF on the result to add searchable text back.
A rotated page takes more space. The image is scaled to fit the original page size and the empty corners are filled white. Crop PDF can trim them.
No. Deskew fixes small tilts only. Use Rotate PDF to turn pages by 90° or 180°.
Last reviewed . See how we build and test our tools, or report an error.
