How to reduce a photo to 50 KB or 20 KB for online forms
Very small limits such as 50 KB or 20 KB are hard to reach by quality alone. Reducing the pixel dimensions first, where the form allows it, does most of the work.
Open the tool with a 50 KB limitWhy small limits are hard
A photo’s file size depends on how many pixels it has and how hard it is compressed. A 24-bit colour image uses about 3 bytes per pixel before compression, so the pixel count sets how much data the compressor must squeeze into your limit.
| Dimensions | Uncompressed size | Ratio for 50 KB | Ratio for 20 KB |
|---|---|---|---|
| 600 × 800 px | 1,440,000 bytes | 28.8 : 1 | 72 : 1 |
| 300 × 400 px | 360,000 bytes | 7.2 : 1 | 18 : 1 |
| 200 × 250 px | 150,000 bytes | 3 : 1 | 7.5 : 1 |
| 150 × 200 px | 90,000 bytes | 1.8 : 1 | 4.5 : 1 |
A ratio of around 10:1 is usually where JPEG still looks acceptable for photos, though it depends on the picture. Detailed images compress less well than plain ones. That is why cutting a 600 × 800 photo to 20 KB looks terrible, while a 200 × 250 version reaches it with little visible loss.
Step by step
- Check the form’s pixel rule. If it states exact dimensions, use them. If it states only a KB limit, you can choose smaller dimensions yourself.
- Crop out unneeded background first. SizeKit does not crop, so use your phone’s editor. Less area means fewer pixels to store.
- Open SizeKit with the 50 KB preset, or use a 20 KB limit. You can also type any custom number.
- Set the dimensions. Start from what the form requires, or something like 300 × 400 for a portrait if it does not say.
- Download JPG and check the file properties for both pixel size and KB.
If it will not fit
- SizeKit stops with an error and keeps your dimensions, rather than quietly shrinking the picture. Lower the pixel size a step at a time if the form allows.
- A photo with a busy background compresses worse than one with a plain background. Retaking it against a plain wall can save a lot of space.
- If the form fixes the dimensions, such as 200 × 230, and the limit is still not reachable, retake the photo with less detail in the background rather than lowering quality further.
Check for a minimum as well. Some forms ask for a range, such as 20–50 KB. SizeKit sets a maximum only, so verify the result is above the minimum too.
What you give up
Smaller files lose fine detail first: hair, text on clothing and skin texture. For ID-style photos that is usually acceptable. Check the final image at normal size, and if the face looks blocky or smeared, raise the dimensions or the limit if the form permits.
For a more relaxed limit see compressing an image to 100 KB, and for why changing only one of KB or pixels is not enough, read KB versus pixels.
Frequently asked questions
What pixel size is a 20 KB photo?
It depends on the photo. As a rough guide a plain portrait of about 200 × 250 pixels can fit in 20 KB, while a much larger image needs very heavy compression and looks poor.
Why is my file bigger than the limit even at low quality?
The pixel dimensions are probably too large for that limit. Reduce the width and height if the form allows it.
Is smaller always accepted?
Not always. Some forms also set a minimum file size, so check the result against both the minimum and the maximum.