The Image Resizing Guide
Pixels, resolution and aspect ratio explained
Changing an image's size looks trivial, but do it wrong and you get a squashed image or needlessly degraded quality. This guide covers what pixels and resolution actually are, how to resize while keeping the aspect ratio, and the right dimensions for each use.
Contents
1. What is a pixel?
A pixel (px) is the smallest unit a digital image is built from. A 1920×1080 image is a grid of 1920 pixels across and 1080 down — 2,073,600 pixels in total, or roughly 2 megapixels.
More pixels means a larger, sharper image. But how big it looks on screen depends on the display's resolution and pixel density (PPI). A 4000px image still looks small on a small screen, and a 300px image blown up on a large screen looks blurry.
2. Resolution vs. PPI
Resolutionmeans the image's pixel count — 1920×1080, for example. PPI(pixels per inch)describes how many pixels are packed into one inch.
For web images PPI is irrelevant — the screen sizes things by raw pixel count. For print it matters a great deal: print images need at least 150–300 PPI.
Bottom line: If the image is going on the web, ignore PPI entirely and just get the pixel dimensions right. If it's going to print, check the DPI setting.
3. Resizing without distorting the image
If you scale width and height by different amounts, the image stretches or squashes. To keep the original proportions, enter only the width or only the height and let the other value be calculated for you.
The ratio formula
If the original is 1920×1080 (16:9) and you want a width of 1200px:
new height = 1200 × (1080 ÷ 1920) = 1200 × 0.5625 = 675px
Turn on ImgFixIt's "Lock aspect ratio" and entering either width or height fills in the other automatically — resizing with no risk of distortion.
Careful: Without the ratio lock, entering arbitrary values like 1200px wide by 600px tall will squash the image. Keep the lock on.
4. What to watch out for when enlarging
Enlarging an image beyond its original size (upscaling) costs you quality. Adding pixels means the software has to guess at data that was never there, and the result looks soft and mushy.
As a rule, avoid enlarging beyond 200%of the original. If you genuinely need high-quality enlargement, use a dedicated AI upscaling tool. ImgFixIt's resize is fast and convenient but isn't built for extreme upscaling.
The key principle: Shrinking always looks better than enlarging. The best move is to shoot or create larger than you need in the first place.
5. Recommended dimensions by use case
| Use case | Recommended size (px) | Ratio |
|---|---|---|
| Blog body images | 1200×800 or 1200×675 | 3:2 or 16:9 |
| Instagram square post | 1080×1080 | 1:1 |
| Instagram portrait post | 1080×1350 | 4:5 |
| Instagram Stories & Reels | 1080×1920 | 9:16 |
| YouTube thumbnail | 1280×720 | 16:9 |
| Naver Blog body | Up to 1200px wide | Any |
| KakaoTalk OpenChat image | 1200×630 | About 2:1 |
| Website banner | 1920×600 or 1600×500 | About 3:1 |
| Profile picture | 400×400 or larger | 1:1 |
| Email images | 600–800px wide | Any |
※ Platform policies change. Check each platform's official guidance for the current numbers.
6. Resizing with ImgFixIt
- Upload your image
- Check "Resize" in the "③ Compress / Resize" step
- Enter the width you want, in pixels
- With "Lock aspect ratio" checked, the height is calculated for you
- Need an exact height? Uncheck the ratio lock and type it in
- Click download to save the resized image
Compress at the same time: Check "Quality Compression" as well to cut dimensions and file size together. Resize is applied first, then compression.