Why 30 KB is such a common limit
Many job, exam and admission portals cap photo uploads at 30 KB, and plenty use the same figure for signatures. It's a practical size for the organisation running the form: big enough for a recognisable face on an admit card or ID card, small enough to store a very large number of applications. The rule tends to come in one of these shapes:
- A plain maximum for the photograph, sometimes with fixed pixel dimensions alongside it.
- A range such as 10–30 KB, where a file that is too small is rejected as well.
- A print size such as 3.5 × 4.5 cm, with 30 KB as the upload limit.
- One rule for two files: the photo and the signature each 30 KB or less.
These are patterns, not the rules of any particular form. Instructions differ between organisations and can change from one cycle to the next, so go by the advertisement or portal instructions you're actually working from.
From cm to pixels: the DPI decides
When a form gives the photo size in centimetres or inches, the number of pixels depends on the DPI you choose, and at 30 KB that choice matters. Here's how common print sizes convert, and roughly the JPG quality a face photo gets at 30 KB:
| Print size | DPI | Pixels | Quality at 30 KB |
|---|---|---|---|
| 3.5 × 4.5 cm | 200 | 276 × 354 | About 92%, the tool's top setting |
| 3 × 4 cm | 300 | 354 × 472 | About 80–92% |
| 3.5 × 4.5 cm | 300 | 413 × 531 | About 75–90% |
| 2 × 2 in | 200 | 400 × 400 | About 80–92% |
| 2 × 2 in | 300 | 600 × 600 | About 45–80% |
The higher figure is for a plain background and the lower one for a busy picture; both come from our own test encodes. The takeaway: at 300 DPI a 3.5 × 4.5 cm photo fits 30 KB well, while a 2 × 2 inch photo at 300 DPI is a squeeze. Unless the form asks for it, avoid 600 DPI for uploads: it has four times the pixels of 300 DPI and leaves very little data for each one.
To make these sizes, use the cm / inch option in the Image Resizer with Crop to fill exact size, then compress here. Or do both at once with the Image Resizer's Limit file size option set to 30 KB, which also keeps the DPI value in the file; this compressor doesn't keep a DPI value when it re-encodes. For the most common size, resize photo to 3.5 × 4.5 cm opens the Image Resizer already set up.
Signatures, thumb impressions and small scans
30 KB is generous for a signature. A clean signature on white paper at typical form sizes, from 140 × 60 to 350 × 150 px, usually comes to well under 10 KB even at high quality. So if your signature file is over 30 KB, it almost always means one of two things: the image is a photo of the whole page, or the paper is grey and shadowed, which JPG has to store as detail.
The fix is to crop and clean rather than compress harder. The Signature Resizer trims the paper down to the ink, turns the background white, outputs exact pixels or cm, and can meet a minimum KB when the form sets a range such as 10–30 KB.
Other small uploads behave a little differently:
- Thumb impressions are like signatures: crop tightly around the print on plain white paper before compressing.
- Part of a document, such as the result block of a mark sheet, can fit 30 KB if you crop to just that area and keep it to around 600–800 px wide.
- A full A4 page is too much for 30 KB as a JPG. Getting there means shrinking it below about 500 px wide at low quality, and small print blurs. Use compress image to 100KB or a PDF if the form allows either.
Worked example: photo and signature for the same form
Suppose a recruitment form asks for a JPG photograph of 3.5 × 4.5 cm and a JPG signature, each no more than 30 KB, and all you have is your phone.
- Take the photo against a plain light wall. In the Image Resizer, set it to 3.5 × 4.5 cm at 300 DPI with Crop to fill exact size, which gives 413 × 531 px.
- Add the resized photo here. With 30 KB already set, the result line should keep 413 × 531 px and show a quality somewhere around 75–90%.
- Sign on white paper with a dark pen and photograph it from directly above. Open that photo in the Signature Resizer, enter the form's signature size and a 30 KB maximum, and download it.
- Upload each file to its own field. If the portal shows a preview, check that neither the face nor the signature is cropped or stretched.
When a 30 KB file is still rejected
If a portal refuses a file the tool says is under 30 KB, the size is rarely the real problem. Check these first:
- How KB is counted. The target keeps files at or under 30,000 bytes, and the size shown on screen counts 1,024 bytes per KB, so a result for a 30 KB target usually reads 29 KB or a little less. Both pass a 30 KB rule. If a portal still says the file is too large, set the target to 28 KB and try again.
- The wrong file. The compressed copy ends in “-compressed”. Make sure that's the one you pick, not the original in your gallery.
- The format. Renaming a PNG or WebP to .jpg doesn't convert it, and strict portals can tell. Choose JPG as the output here to get a real JPEG.
- The dimensions. A form that wants 413 × 531 px may reject a 300 × 386 px file even though it's under 30 KB. Compare the pixel size in the result line with the instructions.
- A minimum size. If the rule is a range, a file can be refused for being too small. The Image Resizer can pad a photo up to a minimum, and the Signature Resizer can do the same for signatures.
30 KB, or 25 KB or 40 KB?
- Choose 25 KB when the form says 25, or for a small photo where you'd like some margin; at 354 × 472 px and below the difference is barely visible. See compress image to 25KB.
- Stay at 30 KB for a 3.5 × 4.5 cm photo at 300 DPI, a signature, or anything the form caps at 30.
- Go to 40 KB only if the form allows it, for example for a larger square photo. It lifts a 600 × 600 px photo from roughly 45–80% quality to about 65–87%. See compress image to 40KB.