How to Resize and Compress Images for Websites, Email and Forms
Updated 27 September 2026 · 5 min read
Most "file too large" errors need two separate fixes: resizing, which changes an image's pixel dimensions, and compressing, which changes how efficiently those pixels are stored. This guide explains the difference, gives sensible targets for websites, email and upload forms, and walks through getting a photo under a size limit.
Resizing and compressing are different jobs
Resizing changes the number of pixels. A 4,000 × 3,000 phone photo holds 12 million pixels; resized to 1,600 × 1,200, it holds 1.92 million, about 16% as many. The file shrinks a lot, and the picture still looks sharp at the size people actually view it. What you can't do is go back: enlarging a small image later doesn't restore the detail.
Compressing keeps the same pixels but stores them more efficiently. For JPG and WebP that means a lower quality setting, which discards detail you're unlikely to notice. The dimensions stay the same.
The order matters: resize first, then compress. Resizing removes most of the excess, and compression fine-tunes what's left. Compressing a huge photo very hard to hit a small limit gives you a blotchy image at full size, which looks worse than a clean, smaller one.
One common confusion: the DPI or PPI number stored in an image only tells a printer how large to print it. Changing it from 72 to 300 without changing the pixels doesn't alter the file size or how the image looks on screen. When a form asks for "300 dpi", it usually means enough pixels to print well at the stated size.
Sensible targets for websites
The rule in Google's web.dev image performance guide is simple: don't send more pixels than the page displays. An image shown in a 500-pixel-wide box needs to be about 500 pixels wide, or twice that to look sharp on high-density phone and laptop screens.
| Use | Width to aim for | File size to aim for |
|---|---|---|
| Full-width banner | 1,920 px | Under about 300 KB |
| Image inside an article | 1,200 to 1,600 px | Under about 200 KB |
| Thumbnail or product grid | 400 to 600 px | Under about 60 KB |
These are starting points rather than rules. A detailed landscape photo needs more bytes than a plain product shot on white. For photos on the web, WebP or JPG at quality 70 to 80 is a good first try; see JPG vs PNG vs WebP for help picking a format.
Sizing images for email
Email services limit the total size of attachments. Gmail's limit is 25 MB, according to Google, and Outlook.com's is also 25 MB, according to Microsoft. Work email limits are set by your company's IT team and are often lower. Limits change, so check with your provider if you're close.
A handful of photos straight off a modern phone can pass that. For someone viewing photos on a screen, 1,600 to 2,000 pixels on the long side is plenty, and at that size a JPG at quality 75 is usually well under 1 MB. Resize before attaching and a whole set of photos fits in one email.
Upload forms with strict limits
Government services, visa applications and job portals often set tight rules for photos and scanned documents. Limits vary between sites and change over time, so always read the instructions on the upload page itself. They usually cover:
- Maximum file size, often given in KB.
- Allowed formats, commonly JPG, sometimes PNG or PDF.
- Dimensions, either exact pixel sizes or a minimum, especially for passport-style photos.
Some sites count 1 MB as 1,000 KB and others as 1,024 KB, so aim for about 10% under the limit to be safe. If the form needs exact dimensions and your photo is a different shape, crop it to the right shape first in your phone's photo editor, then resize. Resizing to a different shape without cropping stretches faces and text.
Step by step: getting a photo under a size limit
Say a job portal asks for a JPG profile photo under 200 KB, and your phone photo is 4,032 × 3,024 pixels and 3 MB.
- Check the format. iPhone photos saved as HEIC won't open in most browsers. Setting Settings > Camera > Formats > Most Compatible makes new photos JPG.
- Crop to the shape the form wants, such as a square, using your phone's editor.
- Resize and compress in one go. Open the Image Compressor, set Save as to JPG, Max width to 800 and Quality to 75, then click Compress Image.
- Check the numbers. The tool shows the original size, the compressed size and how much smaller it is.
- Adjust if needed. Still over? Lower the quality in steps of 10. If the photo starts to look blotchy below about 50, make it smaller instead: set the exact width you need in the Image Resizer, such as 600 pixels, and compress that.
If the form insists on PNG, use the Image Resizer, which keeps the original format. PNG has no quality slider, so smaller dimensions are the only way to cut its size, and the Image Compressor saves only as JPG or WebP.
All of this happens in your browser, so your photos and documents aren't uploaded anywhere. For scanned documents in PDF form, making a PDF smaller works differently.
Social media sizes
For social posts, exact dimensions matter more than file size, because the platforms recompress everything you upload. The Instagram Image Resizer has presets for common sizes: Instagram square (1080 × 1080), portrait (1080 × 1350) and story (1080 × 1920), a WhatsApp profile picture (1200 × 1200), and LinkedIn post (1200 × 627) and cover (1584 × 396) images.
It fits the whole image inside the frame and fills any leftover space with white, rather than cropping. If you want the picture to fill the frame edge to edge, crop it to the same shape first. The result downloads as a JPG.
Frequently asked questions
Does resizing an image reduce its quality?
Making an image smaller removes detail, but at the size it's displayed it looks just as sharp. Making a small image bigger is what causes blur, because the missing detail has to be guessed.
Why is my compressed image bigger than the original?
It was already well compressed, often by the phone or website that created it. The Image Compressor tells you when the result isn't smaller. Keep the original, or try a lower quality or a smaller max width.
How many KB are in an MB?
Either 1,000 or 1,024, depending on the system. That difference is why a file that looks exactly on the limit can still be rejected, so leave a margin.
Are my photos uploaded when I use these tools?
No. The Image Resizer, Image Compressor and social image resizers all work inside your browser, and the result downloads straight to your device.