Where a 300 KB limit turns up
300 KB sits between the tiny limits of photo and signature fields and the roomy limits of general file uploads. It tends to appear where an image has to show real detail but the site still wants to keep storage and pages light:
- Supporting images on application forms: a photo of a certificate, an address proof, a fee receipt or a property, where the form sets a cap per file. The applicant photo and signature fields on the same form usually have much smaller limits of their own.
- Marketplace and classified listings: item photos that buyers will zoom into, on sites and apps that limit the size of each image.
- Websites and content management systems: blog and page images, where many site owners set a budget per image so pages open quickly on mobile data.
- Internal systems: school or office portals and intranets with a modest upload cap.
The number on the form is the rule that counts. If one field allows 300 KB and another only 50 KB, compress each image for its own field; for the small ones, see compress image to 50KB.
What happens to a phone photo at 300 KB
A 12-megapixel phone photo is 4032 × 3024 pixels and usually weighs 3–5 MB. Getting it to 300 KB means cutting the file by roughly 90–94%, and the compressor does that in a fixed order:
- It first tries to keep every pixel and lower only the JPG quality.
- If even a low quality setting (35%) is still over 300 KB, it reduces the dimensions in steps, in proportion to how far over the limit the photo is.
- At the new size, it searches again for the highest quality that stays under 300 KB.
For a full-size phone photo, that usually means the dimensions come down by a moderate amount and the photo is saved at a quality not far above the 35% floor. On a phone screen it looks fine. Zoom in, though, and you may see blotchy skies or smeared fine detail, because quality had to drop to keep all those pixels.
The line under each file tells you which case you're in. A note such as Quality 62% means the dimensions were kept, while Dimensions reduced to fit 300 KB means they weren't. The pixel size is shown alongside, as the original followed by the new size.
Pick the width yourself for a cleaner photo
If the photo will only ever be shown at a modest size, you get a better-looking file by giving up pixels on purpose. Fewer pixels share the same 300 KB, so each one can be stored at a higher quality. Turn on Limit width in the settings and enter a maximum width:
| Where the photo goes | Maximum width to try | Why |
|---|---|---|
| Marketplace or classified listing | 1600 px | Enough for buyers to zoom in on a phone |
| Blog post or web page | 1200–1600 px | Covers typical content columns, including sharp phone screens |
| Photo of a one-page document | 1400–1600 px | Keeps normal-sized print readable |
| Full-screen gallery or slideshow | 1920 px | Fills a Full HD screen |
Limit width counts the width only. A portrait photo limited to 1600 px wide will be about 2130 px tall. The setting never enlarges anything: a photo already narrower than your number keeps its size.
When the note under a file changes from Dimensions reduced to a quality figure, the width you chose fits within 300 KB without any further shrinking. If the quality figure is still low, try a smaller width.
Worked example: six iPhone photos for a listing
You're selling a bookshelf. You take six photos on an iPhone, which saves them as HEIC files of around 2–3 MB each, and the listing form accepts JPG images of up to 300 KB.
- Open this page on the phone or computer that has the photos and add all six. With the output format left on Same, HEIC photos are saved as JPG automatically.
- Turn on Limit width and enter 1600. All six photos are processed again as soon as you change the setting.
- Check each line: you want a quality figure rather than a note about reduced dimensions, and a size a little under 300 KB.
- On a phone, save the photos with the download button on each line: single JPGs are easier to pick in a listing form than a ZIP. On a computer, Download all (6) gives you one ZIP file.
Each file keeps its original name with -compressed added, such as IMG_4127-compressed.jpg, so you can tell the copies from the originals.
Compress, resize, or both?
Compression is the right tool when the only rule is the file size. When the form also sets pixel dimensions, compressing alone won't get you there, because the compressor chooses the dimensions itself.
- Only a KB limit, for example any JPG up to 300 KB: use this page.
- Exact pixels and a KB limit, for example 800 × 600 px and no more than 300 KB: use the Image Resizer, which crops or fits the photo to the exact size and can apply the KB limit in the same step.
- A minimum size, for example at least 1000 px wide: if you use Limit width, set it no lower than the minimum, then confirm the new dimensions on the result line.
- A PDF instead of an image: place the compressed JPG in a PDF using JPG to PDF. If you already have the PDF, compress PDF to 300KB is the page you need.
Why the size reads 293 KB, and other details
- The size looks lower than 300. The compressor keeps each file at or under 300,000 bytes, which passes a form whether it counts a kilobyte as 1,000 or 1,024 bytes. This page and Windows File Explorer show sizes in units of 1,024 bytes, so a file right at the limit reads as about 293 KB. That's expected, not a mistake.
- Already small enough. A photo that's under 300 KB to begin with, in the same format and without Limit width shrinking it, is passed through untouched and marked as kept. It isn't saved again, so it loses nothing.
- PNG screenshots. Screenshots stay PNG unless you change the output. PNG files are made smaller by using fewer colours, a method that keeps text edges sharp. For a photo that happens to be saved as PNG, choose JPG output: it will usually look far better at 300 KB.
- WebP. It suits your own website, if the site supports the format. For forms and listings, stay with JPG unless WebP is listed. A greyed-out WebP option means your browser can't create WebP files.