How to Reduce Photo File Size: What Really Works for 100 kB, 200 kB and 500 kB
Lowering the quality alone barely helped our phone photos, and at higher settings they even got bigger. We measured which combination of size and quality fits common upload limits.
Upload forms often set strict limits: a profile photo of at most 200 kB, an application document under 1 MB, an email attachment that should not fill the recipient's inbox. Most people first lower the quality slider and are surprised when the file hardly shrinks. We measured why. We took three ordinary phone photos and a screenshot, saved them again in Chrome 141 with many combinations of size, quality and format, and compared every result with the original. Our image compressor uses the same browser function, so in Chrome it produces the same files. In other browsers the numbers can differ slightly, because each browser has its own encoder.
The test photos
The three photos come from a family celebration and show a cake on a table, a decorated wall and a snack platter. Each has 2,576 × 1,932 pixels, about 5 megapixels (the cake photo is upright), and they weigh 506, 738 and 622 kB. An analysis of the files showed that they had already been saved as JPG at a quality of about 75. We used them only for measuring and do not publish them.
To compare quality we used SSIM (structural similarity), a standard measure that compares the structure of two images: 1 means identical, and above about 0.97 differences are hard to see at normal viewing size. In all tables, 1 kB is 1,000 bytes.
Lowering the quality alone hardly helps
First we saved the photos again at their full size and only changed the quality:
| Quality | File size compared with the original | SSIM |
|---|---|---|
| 95 | 148–158% | 0.999 |
| 90 | 121–124% | 0.997 |
| 80 | 103–104% | 0.994–0.995 |
| 75 | 97–98% | 0.999 |
| 70 | 94–96% | 0.994–0.995 |
| 60 | 85–86% | 0.978–0.984 |
| 50 | 75–76% | 0.948–0.965 |
At 90 or 95 the files became up to 58% bigger without getting any better: detail that the first save removed cannot come back. At 75, the quality of the originals, the new files were almost identical to them (SSIM 0.999) and only 2 to 3% smaller. Real savings started only at 50 to 60, and even then the photos still weighed 430 to 634 kB at quality 60. If a photo has already been compressed once, the quality slider is the wrong lever.
Reduce the pixels first
The number of pixels decides the file size much more than the quality setting. We reduced the photos so that their longer side had a certain length and saved them at quality 75:
| Longer side | Megapixels | Cake / wall / platter | Compared with the original |
|---|---|---|---|
| 2,576 px (original size) | 5.0 | 492 / 720 / 612 kB | 97–98% |
| 1,920 px | 2.8 | 305 / 411 / 369 kB | 56–60% |
| 1,600 px | 1.9 | 226 / 295 / 274 kB | 40–45% |
| 1,280 px | 1.2 | 157 / 195 / 190 kB | 26–31% |
| 1,024 px | 0.8 | 110 / 132 / 135 kB | 18–22% |
| 800 px | 0.5 | 74 / 86 / 91 kB | 12–15% |
Halving the longer side leaves a quarter of the pixels, and the files shrank to 26 to 31% of their original size. For many uses that is still plenty: 1,280 pixels are enough for an email or a picture in a column of text, 800 pixels for a profile picture or a preview. For a photo that should look sharp across the full width of a website on high-density screens, our guide JPG, PNG, WebP or AVIF? recommends about twice the display width.
Settings for common size limits
From these measurements we chose settings that kept all three photos below common limits:
| Limit | Longer side | JPG quality | Cake / wall / platter |
|---|---|---|---|
| 500 kB | 1,920 px | 80 | 355 / 475 / 425 kB |
| 300 kB | 1,600 px | 75 | 226 / 295 / 274 kB |
| 200 kB | 1,280 px | 75 | 157 / 195 / 190 kB |
| 150 kB | 1,024 px | 75 | 110 / 132 / 135 kB |
| 100 kB | 800 px | 75 | 74 / 86 / 91 kB |
Our image compressor can now do this search for you: enter the limit in the new Target size field. The tool tries quality levels between 60 and 90 and keeps the highest one that fits. If even 60 is too big, it reduces the dimensions step by step and tries again. For our photos it chose these settings:
| Photo | Target 200 kB | Target 100 kB |
|---|---|---|
| Cake (upright) | 1,252 × 1,670 px, quality 64: 194 kB | 829 × 1,106 px, quality 62: 97 kB |
| Wall | 1,375 × 1,031 px, quality 68: 193 kB | 980 × 735 px, quality 64: 99.5 kB |
| Platter | 1,495 × 1,121 px, quality 64: 199 kB | 993 × 745 px, quality 60: 99 kB |
The tool keeps more pixels and uses a lower quality than our table. Both approaches are reasonable, because, as the next section shows, the difference between 60 and 80 is very hard to see.
How low can the quality go?
To see where compression becomes visible, we saved the 1,280-pixel version of the cake photo at quality 80, 60, 40 and 25 and enlarged the same details four times. 80 and 60 looked practically the same, even in the glittery decoration and the soft curtain in the background. At 40, faint square blocks appeared in soft, even areas. At 25 they were obvious, and gentle colour transitions turned into flat patches. These squares are typical of JPG, which compresses an image in blocks of 8 × 8 pixels.
For photos, 60 to 80 is therefore a safe range. If a file is still too big at 60, reduce the dimensions further rather than lowering the quality: a slightly smaller picture is less noticeable than blocks. Our target size option works the same way.
WebP: smaller, but not accepted everywhere
We also saved the photos as WebP and compared the file sizes at the same measured quality, an SSIM of 0.97:
| Photo | 1,600 px: JPG → WebP | 1,280 px: JPG → WebP |
|---|---|---|
| Cake | 215 → 197 kB (−8%) | 161 → 143 kB (−11%) |
| Wall | 396 → 292 kB (−26%) | 259 → 182 kB (−30%) |
| Platter | 288 → 253 kB (−12%) | 196 → 167 kB (−15%) |
WebP saved 8 to 30%, most on the detailed wall photo. In our guide JPG, PNG, WebP or AVIF?, measured with other photos and another encoder, the average was 26%; how much you save depends on the picture. For your own website, WebP is a good choice. For forms, authorities and email, JPG is the safer format, because some upload forms still accept only JPG or PNG.
Screenshots need a different approach
A screenshot has sharp text and large even areas, the opposite of a photo. We tested a 1,280 × 1,200-pixel screenshot of one of our guides, saved as PNG with 288 kB:
| Saved as | File size | SSIM |
|---|---|---|
| PNG, saved again by the browser | 421 kB | 1 (identical) |
| JPG, quality 90 | 237 kB | 0.994 |
| JPG, quality 80 | 183 kB | 0.986 |
| WebP, quality 100 | 217 kB | 1 (identical) |
| WebP, quality 90 | 139 kB | 0.998 |
| WebP, quality 80 | 106 kB | 0.996 |
Saving the PNG again in the browser made it 46% bigger; PNG files from different programs differ a lot in how tightly they are packed. Our compressor notices this and keeps the original. WebP at quality 80 was the clear winner: 63% smaller than the PNG and still closer to the original than JPG at 90. At three times magnification, the text was easy to read in every version. If a form accepts only JPG, use quality 90 for screenshots.
What gets lost along the way
When a browser saves an image again, it creates a new file from the pixels. In our test, Chrome kept the colour profile but removed:
- EXIF data, such as the camera model, the date and, if present, the GPS location. That is useful before you share photos publicly.
- The HDR gain map. All three photos were Ultra HDR images: besides the normal picture, they contained a small second image (2 to 4% of the file) that lets HDR screens show highlights brighter. After compression they look like normal photos there.
Nothing that is part of the picture itself is removed. A date stamp printed into the photo, as on one of ours, stays visible. If you need to hide something, crop it away before compressing.
Step by step: a photo for an upload limit
- Keep the original and work on a copy. Every lossy save removes a little more detail.
- Crop away what you do not need with the Crop Image tool. Every pixel removed saves space.
- Open the image compressor and choose JPG for forms and email, or WebP for your own website.
- Enter the limit as the target size, for example 200 for 200 kB. If you prefer fixed settings, use the table above or set the size first with the image resizer.
- Check the result at 100% zoom, especially faces and text.
- For screenshots, choose WebP, or JPG at quality 90 if only JPG is accepted.
Tools used in this guide
-
Image Compressor
Compress JPG, PNG and WebP images in your browser. Choose the quality, shrink dimensions and download smaller files – no upload needed.
Open tool -
Image Resizer
Resize images to exact pixel dimensions or by percentage, with or without keeping the aspect ratio. Free, fast and private.
Open tool -
Crop Image
Crop JPG, PNG and WebP images online: drag a frame or enter exact pixels, with ratios like 1:1, 4:3 and 16:9. Free, no upload.
Open tool -
Image Converter (JPG, PNG, WebP)
Convert images between JPG, PNG and WebP right in your browser – for example PNG to JPG or JPG to PNG. Batch conversion, no upload.
Open tool
Frequently asked questions
How do I reduce a photo to 100 kB?
Enter 100 as the target size in our image compressor. Without that option, reduce the longer side to about 800 pixels and save the photo as JPG at quality 75. Our three 5-megapixel test photos then weighed 74 to 91 kB.
Why did my photo get bigger after compressing?
Because it had already been compressed. Saving a JPG again at a higher quality than before only adds data: our phone photos, saved at about 75, grew by 21 to 24% at quality 90. Our compressor keeps the original if the result would be bigger at the same size and format.
Is 1 kB 1,000 or 1,024 bytes?
According to the international standard, 1 kB is 1,000 bytes and 1,024 bytes are a kibibyte (KiB). Windows and some forms still count 1,024. A file that is below a limit counted with 1,000 bytes is also below it with 1,024, which is why our target size uses 1,000.
Does compressing remove the location from my photos?
In our test, Chrome removed all EXIF data when saving, including any GPS coordinates. Anything printed into the picture itself, such as a date stamp, stays.
Is WebP or JPG better for small files?
WebP was 8 to 30% smaller in our test at the same quality. Use it for your own website; use JPG for forms, email and printing, because not every recipient accepts WebP.
Are my photos uploaded?
No. Our image tools run in your browser. Your photos are processed on your own device and never sent to our server.
Sources and further reading
- MDN Web Docs: HTMLCanvasElement.toBlob() – the browser function our image tools use to save images (developer.mozilla.org)
- Android Developers: Ultra HDR Image Format v1.1 (gain map stored next to the normal JPG image) (developer.android.com)
- Wang, Bovik, Sheikh, Simoncelli (2004): Image quality assessment: from error visibility to structural similarity (SSIM). IEEE Transactions on Image Processing 13(4) (doi.org)