Aspect ratios explained: how to calculate and resize without distortion
How to reduce any width and height to a ratio, find a missing dimension, and decide between scaling, cropping and padding.
An aspect ratio describes the shape of an image or video, not its size. A 1280×720 video and a 3840×2160 video have the same shape, 16:9. Knowing the ratio lets you resize without stretching and plan crops before you export.
What a ratio tells you
The ratio is width compared with height. 16:9 means 16 units wide for every 9 units high. The decimal form, width divided by height, is useful for comparisons: 16:9 is about 1.78, 4:3 is about 1.33 and 1:1 is exactly 1. Values below 1 are portrait, above 1 are landscape.
Calculating a ratio by hand
Divide both sides by their greatest common divisor (GCD), the largest number that divides both exactly. For 1920×1080 the GCD is 120, so the ratio is 1920÷120 : 1080÷120 = 16:9.
Some sizes do not reduce neatly. 1366×768 reduces to 683:384, which is close to, but not exactly, 16:9. That is why calculators also show the nearest common ratio.
Open the Aspect Ratio CalculatorReduce any size to a ratio and see the nearest common one.Finding a missing side
Cross-multiply: new height = new width × ratio height ÷ ratio width.
16:9 at 1280 px wide → 1280 × 9 ÷ 16 = 720 px high
9:16 at 1920 px high → 1920 × 9 ÷ 16 = 1080 px wideRound to whole pixels. Many video encoders also prefer even numbers.
Scale, crop or pad
When the source and target ratios differ, there are only three honest options:
- Scale to fit, keeping the ratio. The image fits inside the target but leaves empty space on two sides.
- Crop to the new ratio. The frame is filled, but part of the image is cut off. Decide what must stay in frame first.
- Pad with a background color or blurred fill (letterboxing). Nothing is lost, but the bars are visible.
Stretching, which means changing width and height independently, distorts faces and text, and is almost never the right answer. The Image Resizer locks the ratio by default for this reason.
Common ratios
| Ratio | Decimal | Typical use | Example size |
|---|---|---|---|
| 16:9 | 1.78 | Widescreen video, monitors, presentations | 1920×1080 |
| 9:16 | 0.56 | Vertical short-form video and stories | 1080×1920 |
| 1:1 | 1.00 | Square posts, profile pictures | 1080×1080 |
| 4:5 | 0.80 | Portrait feed posts | 1080×1350 |
| 4:3 | 1.33 | Tablets, older displays, many phone photos | 1600×1200 |
| 3:2 | 1.50 | Photos from most interchangeable-lens cameras | 6000×4000 |
Social platforms change their recommended sizes from time to time. Check the platform’s current help pages before a campaign, then use the ratio to produce the exact pixels.