Where the megabytes come from
A phone camera saves a photo as a JPEG of 12 to 50 megapixels. Twelve megapixels is 4,000 by 3,000 pixels, and at the quality phones use that is 3 to 5 MB; a 48-megapixel photo is often 8 MB or more. A government portal, a job site or an email attachment limit of 100 KB, 50 KB or 20 KB is asking for a file thirty to four hundred times smaller.
That sounds brutal, but think about what the form does with the photo. It shows it in a box 300 to 600 pixels wide, or prints it at 3.5 by 4.5 cm. Either way it throws away more than nine tenths of the pixels on arrival. Sending them does nothing except push the file over the limit. The same is true of the camera’s extra data: the EXIF block with the GPS position, the date, the phone model and a small preview can be tens of kilobytes on its own, which is a fifth of a 100 KB budget.
So a photo has three things that cost bytes, and they are not equal:
| What you change | What it does | Typical effect on the file |
|---|---|---|
| Pixels (width and height) | Fewer pixels to store | 4,000 px wide to 1,600 px wide removes about 85% of the pixels and most of the bytes |
| Quality (JPEG and WebP) | How much fine detail the encoder keeps | Quality 100 to 80 roughly halves the file with no visible change on a screen |
| Format | How cleverly the detail is packed | WebP is about 25 to 34% smaller than JPEG at the same visual quality (Google’s own study of 11,000 images) |
Pixels first, quality second, format last. Do it the other way round, quality first, and you end up with a huge blurry picture: all the pixels are still there, but each one has been smeared.
Step one: decide how many pixels the form needs
Ask what the photo is for, and size it for that.
- A photo on a form or an ID card: 600 pixels on the short side is plenty. A passport-style photo printed at 35 by 45 mm needs about 420 by 540 pixels at 300 dots per inch; many portals ask for exactly that range.
- A photo in an email or a chat: 1,200 to 1,600 pixels on the long side looks sharp on any phone and most laptops.
- A photo for a website: the width it is shown at, times two for high-density screens. A 600 pixel column wants a 1,200 pixel image.
- A scan of a document: 1,500 to 2,000 pixels on the long side keeps small print readable. Below 1,200 the text starts to break up.
Resizing from 4,000 pixels to 1,200 keeps 9% of the pixels, and the file drops by a similar share before you touch the quality. This is the single biggest saving you will make, and it costs nothing visible, because the form could never show those pixels anyway.
Try it: Resize Image
Set the width in pixels or a percentage, keep the proportions, and see the new size before you download.
Step two: lower the quality, but only to 75 or 80
JPEG quality is a number from 1 to 100, and it is not a percentage of anything. Between 100 and about 90 the file shrinks fast while the picture does not change visibly, because the encoder stops storing noise the camera sensor added. Between 90 and 75 it keeps shrinking and you still cannot tell on a screen. Below 70 you start to see blocks in smooth areas like skin and sky, and halos around sharp edges like text. Below 50 everything looks like it was faxed.
For a photo that will be looked at, stop at 75 to 80. For a scan of a document that only has to be legible, 60 is fine, because text has no smooth areas to show the blocks.
Two photos with the same pixels and the same quality can still differ three to one in size. JPEG spends bytes on detail: foliage, fabric, gravel and crowds have detail everywhere and stay large; a face against a plain wall, or a page of text, compresses well. That is why a size target cannot be set directly. It has to be searched for.
Step three: pick the format the receiver accepts
JPEG is accepted everywhere, and for a form it is the safe choice. WebP makes files about a quarter to a third smaller at the same quality, and every current browser shows it, but some government and bank portals still refuse anything but JPEG, so use it for your own website, not for applications. PNG is the wrong format for photographs: it stores every pixel exactly, so a photo as PNG is five to ten times larger than as JPEG. Use PNG for screenshots, logos and diagrams with flat colours and sharp text, which JPEG smears.
How the compress-to-size tools get under a limit
Typing “100 KB” into a quality box does not work, because the size depends on the photo. The size pages on this site search instead. The tool starts from a sensible width, encodes the photo at a quality, measures the result, and moves the quality up or down until the file sits just under the limit. If even the lowest acceptable quality is too big, it reduces the width and tries again, so the photo loses pixels rather than turning into blocks. It also drops the EXIF block, which is why the location and date are not in the result.
Everything happens inside your browser with its own image encoder. The photo is not uploaded, which matters when the photo is of your passport or your face.
Try it: Compress Image to 100 KB
Also available for 50 KB and 20 KB. The tool finds the quality and width that fit and shows the size before you download.
What each target can hold
These are typical results for an ordinary phone photo of a person. Photos with a lot of fine detail land smaller in pixels at the same limit, which is why the tool searches rather than assumes.
| Target | What fits comfortably | What it is good for |
|---|---|---|
| 100 KB | About 800 by 1,000 pixels at quality 80 | Visa and job portals, ID photos, a photo on a CV, a sharp email attachment |
| 50 KB | About 600 by 750 pixels at quality 75 | Exam and university forms, profile pictures, a document scan that only has to be read |
| 20 KB | About 350 by 450 pixels at quality 70 | Signature and thumbnail boxes, forms that show the photo very small |
At 20 KB a face is still clear; a page of small text is not, so for a document scan with a 20 KB limit, crop to the part of the page that matters before compressing.
Checks before you upload
- Open the result at full size. A downloaded file that looks fine as a thumbnail can be blocky at 100%. Look at the skin and the edges of text.
- Read the form’s limits again. Many forms set a pixel range as well as a size, for example “between 600 and 1,200 pixels square”. Resize to that first, then compress.
- Check the unit. Some forms count a kilobyte as 1,024 bytes. The tools here stay under the limit by either reading, so a file they call 100 KB passes both.
- Keep the original. Compression throws detail away for good. Compress a copy, and keep the original photo on your phone for the next form.
Frequently asked questions
Is 1 KB 1,000 bytes or 1,024 bytes?
Both readings are in use. Windows shows sizes in units of 1,024, most web forms and the site’s tools count 1,000. The compress-to-size pages stay under the limit by either reading, so a file they call 100 KB passes a form that counts in 1,024s too.
Will a 100 KB photo still print well?
For a passport-size print or a photo on a form, yes: at 600 by 800 pixels and quality 80 a photo is about 100 KB and prints cleanly at 5 by 7 cm. For an A4 print you want 2,000 pixels or more on the long side, which no photo fits into 100 KB.
Does compressing a photo remove the location data?
The compress and resize tools on this site re-encode the picture through the browser, which writes a fresh file without the camera’s EXIF block, so the GPS position, the date and the phone model are not in the result. Other tools may keep it; check the file’s properties if that matters.
Why does the same quality setting give different sizes for two photos?
JPEG spends bytes on detail. A photo of foliage, fabric or a crowd has detail everywhere and compresses badly; a photo of a face on a plain wall compresses well. Two photos with the same pixels and quality can differ in size three to one, which is why a size target has to be searched for, not set.
Should I use WebP or JPEG for a form?
JPEG unless the form says otherwise. Every government portal, bank and job site takes JPEG; a few still refuse WebP. WebP is the better choice for your own website, where it is about a quarter to a third smaller at the same quality.
Written by Saad Naeem
AI engineer in Doha who builds every tool on ToolboxHere. The figures in the guides come from the official sources named in them or from the tools themselves. Found a mistake? Tell us and it is corrected.