How to Reduce Image and PDF File Size for Uploads and Email
Application portals, email services and forms love file size limits: 50 KB for a signature, 200 KB for a photo, 2 MB for a document. Phone cameras and scanners produce files that are far larger than that. The good news is that most of the size is detail nobody can see on a screen. This guide shows how to cut file size sensibly, and what to do when a document is still too big.
Why files are so big
A modern phone photo is around 4000 × 3000 pixels, which is 12 million pixels, while a typical laptop screen shows about 2 million. A photo also stores a lot of fine colour information, plus extra data such as the camera model and GPS location. Reducing the pixel dimensions and applying a sensible amount of compression removes the surplus.
The three levers for images
- Dimensions. Halving the width and height of a photo cuts the pixel count to a quarter. For a web page or form upload, a longest side of 1200 to 2000 pixels is usually plenty.
- Quality. For JPG, WebP and AVIF, quality 60 to 80 usually gives a big saving with little visible difference. Below about 50, blur and blocky patches become noticeable.
- Format. Photographs are best as JPG or WebP. Screenshots, logos and diagrams with flat colour are often smaller and sharper as PNG. A photo saved as PNG is often several times larger than the same photo as JPG.
Hitting a specific limit such as 100 KB
- Start with the original file, not a copy that has already been compressed.
- Set a maximum dimension of about 1200 pixels, and compress at quality 70.
- Check the size. If it is still too big, lower the maximum dimension to 1000 or 800 pixels before you lower the quality much further.
- If it is under the limit by a lot, raise the quality a little for a better-looking result.
For a signature or a passport-style photo, crop it first so that the subject fills the frame, because cropping away empty space reduces size without costing any quality in the part you keep.
Turning images into a PDF without a huge file
When you turn photos of documents into a PDF, each photo is stored at full quality, so ten phone photos can easily make a very large PDF. Compress and resize the images first, then convert them. Choosing A4 pages makes a tidy printout, while matching the page size to each image keeps the original shape.
When a PDF is too large
- Scans are the usual culprit. If you scan, choose a resolution of around 150 to 200 dpi in black and white or greyscale for text documents. That is usually readable, and far smaller than a 600 dpi colour scan.
- If you create the PDF from a word processor, look for an export option that reduces image quality or “minimum size”.
- Split the document into parts, for example each section, and send or upload the parts separately if the limit allows multiple files.
- Remove pages you do not need before sending.
Combining documents for portals that want one file
Many portals want a single PDF with everything in it. Merge your documents in the order the portal asks for, and open the result to check that the order is right before uploading. If the merged file is too big, shrink the images in each source file first.
A few cautions
- Keep your originals. Lossy compression cannot be undone, and compressing the same JPG again and again keeps degrading it.
- Do not upload IDs, financial documents or anything confidential to a web service unless you are comfortable with that. Files on this site are processed on our server and deleted automatically, but they do leave your device.
- Re-saving an image normally removes location data such as GPS, which is a privacy benefit when you share photos.
Tools mentioned in this guide
- Compress image: Make photos and images smaller for the web or email while keeping them looking good.
- Images to PDF: Turn JPG, PNG and other images into one PDF, one image per page.
- Merge PDFs: Combine several PDF files into one document, in the order you choose.
- Split PDF: Split a PDF into separate files by page range, or into equal parts.
- Resize, crop & rotate: Resize, crop and rotate a picture, with ready-made sizes for social media.