Phone photos are now thousands of pixels wide and several megabytes each, so application systems often reject them as too big. Here are the units those systems use, the sizes real systems ask for, and how to shrink a photo so it passes.
In short
- Limit in pixels, such as no more than 240×240: use the image resizer and set the long side in pixels.
- Limit in KB or MB: use the image compressor to cut the file size.
- JPG only, but your photo is HEIC or PNG: use the image converter.
Every tool runs in your browser and handles several photos at once. Your photos are not uploaded.
Pixels, KB and dpi
- Pixels (px) are the dots in the image, such as 240×240. Adobe says file size is directly proportional to pixel dimensions: more pixels, bigger file.
- KB / MB is the file size, which depends on both the pixel count and how hard the image is compressed.
- ppi or dpi, in Adobe’s words, is the number of pixels per inch for print quality. It converts pixels into centimetres on paper; it doesn’t make an image sharper on screen.
Centimetres to pixels: pixels = centimetres ÷ 2.54 × ppi. A 3×4 cm photo at 300 ppi is about 354×472 pixels, matching KMUTT’s upload guide, which asks for about 351×472 pixels (document size 3×4 cm) at 300 pixels per inch. That guide dates from 2015, so treat it as an example of the arithmetic.
What real systems ask for
| System | Requirement |
|---|---|
| OCSC general exam (ภาค ก.), 2569 | A .JPG of at least 40 KB; front-facing, no hat or dark glasses, taken within 6 months, plain background. Without a photo you can’t pay the fee |
| myTCAS | Recommended: plain background such as white or blue, no more than 240×240 pixels or 10–100 KB; glasses are fine as long as it looks like you now |
| Thai e-Visa | .JPG or .JPEG up to 3 MB, taken within six months |
Some systems set a minimum too: the OCSC wants at least 40 KB, so over-compressing can fail as well. Read the current announcement for the system you’re applying to, since requirements differ between systems and years.
What social platforms use
| Platform | What it says |
|---|---|
| Uploads up to 1080 pixels wide, aspect ratio between 1.91:1 and 3:4 (1080 wide, 566–1440 tall); larger photos are sized down to 1080 wide, and ones under 320 are enlarged to 320 | |
| Facebook Page profile picture | 320×320 pixels for best quality |
| Facebook Page cover | At least 400×150; loads fastest as an sRGB JPG 851 wide, 315 tall and under 100 KB; PNG may look better with a logo or text |
| LINE (images sent via the Messaging API) | JPEG or PNG up to 10 MB; rich menu images 800–2500 pixels wide and up to 1 MB |
The LINE figures come from its developer documentation for official accounts, not limits for personal chats.
Resizing step by step
To hit a pixel size
- Open the image resizer and choose your photos (several at once is fine).
- Shrink to 75%, 50% or 25%, or set the long side in pixels, such as 240 for myTCAS or 1080 for Instagram.
- Download. The aspect ratio is kept, so if a system wants a square, crop the photo square first.
The tool only shrinks, because enlarging adds no real detail.
To get the file under a size in KB
- Open the image compressor and choose your photos.
- Adjust the quality and check the resulting size.
- If it’s still too big, reduce the pixel size with the resizer first, then compress again.
Compressed photos come out without EXIF data, such as the camera model and GPS coordinates, which helps privacy.
File type: MDN explains that JPEG is lossy and a good fit for photographs, while PNG is lossless and better for screenshots, diagrams and line art. If a system takes JPG only, convert first with the image converter.
Sending by e-mail
Google says personal Gmail accounts can attach up to 25 MB in total; above that, Gmail replaces the attachments with a Google Drive link. Resizing first keeps everything in one e-mail.
Note
This article is based on the OCSC announcement, myTCAS, the Ministry of Foreign Affairs’ e-Visa guide, KMUTT’s upload guide and help pages from Instagram, Facebook, LINE Developers, Adobe, MDN and Google, read on 30 September 2026. Requirements change from year to year; follow the latest announcement of the system you apply to.
