In this article
A photo is 4000 wide and 3000 tall. You need it 1200 wide for a website. What height keeps it undistorted? If you guessed 900, you already understand aspect ratios. If you typed 1000 and the people turned thin, this article is for you.
An aspect ratio is only the shape of a frame: how wide it is compared with how tall. It says nothing about the number of pixels. A phone screenshot and a poster can share a ratio even though one is tiny and one is enormous.
What 16:9 actually means
A ratio of 16:9 means that for every 16 units of width there are 9 units of height. Shrink or grow the frame, and as long as that relationship holds, the shape is the same. 1920 × 1080 is 16:9. So is 1280 × 720, and so is 3840 × 2160, the usual “4K” screen.
Every frame is fitted into the same square so you can compare the shapes. The numbers say nothing about size, only about proportion.
The one calculation you need
This is what the little padlock between the width and height boxes does in most editors. With it locked, the program does exactly this sum for you. With it unlocked, you decide both numbers, and the picture stretches to fit.
Three things you can do when shapes do not match
Sooner or later you need a picture to fit a frame of a different shape. There are only three honest options.
- Crop. Cut away the parts that do not fit. The picture stays undistorted, but you lose content.
- Pad. Keep the whole picture and fill the leftover space with bars or a background. Nothing is lost, but the picture looks smaller.
- Stretch. Squash or pull the picture to fill the frame. It fits perfectly, and everything looks wrong. Almost never the right choice.
- Circles turn into ovals
- Faces look thin
- People notice immediately
- Shapes stay correct
- You choose what to keep
- Crop loses edges, padding adds bars
If you have to choose, crop for impact and pad when the whole picture matters.
How much you lose when you crop
Turning a wide picture into a tall one is the harshest crop. Take a 1920 × 1080 video frame, which is 16:9, and cut it to 9:16 for a vertical format. The new frame must be 1080 tall and only about 608 wide. Almost seven tenths of the picture disappears.
Calculated from the width that remains when the height is kept: 1440, 1080, 864 and 608 pixels out of 1920.
Cameras have the same problem. A 6000 × 4000 photo is 3:2. To make it 16:9 you keep the full width and cut the height to 3375, losing 625 rows, about 16 percent. A 4:3 phone photo at 4000 × 3000 becomes 4000 × 2250 in 16:9, losing a quarter of the frame.
Sizes people look for most
| Where it is used | Ratio | Common size in pixels |
|---|---|---|
| Full HD video, YouTube | 16:9 | 1920 × 1080 |
| HD video | 16:9 | 1280 × 720 |
| Square post | 1:1 | 1080 × 1080 |
| Portrait feed post | 4:5 | 1080 × 1350 |
| Stories, Reels, Shorts | 9:16 | 1080 × 1920 |
| Classic monitor or slide | 4:3 | 1024 × 768 |
These are the commonly recommended sizes. Platforms change their rules from time to time, so check the current guidance before you export something important.
Why 4K is not 4000
The shape matters more than the number of pixels. A 3840 × 2160 screen has four times the pixels of a 1920 × 1080 one, yet exactly the same 16:9 proportions. Doubling both sides quadruples the pixel count. This is why scaling a picture up by 2× makes the file roughly four times larger.
Questions people ask
What is an aspect ratio?
The proportion between a frame’s width and its height, written like 16:9. It describes shape, not size.
How do I resize an image without distorting it?
Keep the aspect ratio locked. New height = new width × (old height ÷ old width). For 4000 × 3000 at 1200 wide that gives 900.
What is the aspect ratio of 1920 × 1080?
16:9. Divide both numbers by 120 to get 16 and 9.
How do I crop a 16:9 video to 9:16?
Keep the full height and cut the width to height × 9 ÷ 16. For 1080 tall that is about 608 pixels wide, so you keep roughly 32 percent of the original width.
Is cropping or padding better?
Crop when the edges are not important and you want the subject to fill the frame. Pad when every part of the picture matters, such as a logo or a chart.