How this aspect ratio calculator works
An aspect ratio describes the shape of an image or screen — the relationship between its width and its height — independent of how big it is in pixels. It is written as two numbers separated by a colon, such as 16:9, which means 16 units of width for every 9 units of height.
To resize without distortion you keep that proportion fixed. Lock a ratio of width rw to height rh, then if you set a new width the matching height is height = width × rh ÷ rw; if you set a new height the matching width is width = height × rw ÷ rh. Going the other way, to find the ratio of a known resolution you divide both pixel values by their greatest common divisor (GCD), which reduces them to the smallest whole-number pair.
Reference note: simplification uses integer pixel values and the Euclidean GCD. Resolutions that do not reduce to a tidy common ratio (such as 1366×768) are matched to the nearest well-known ratio by comparing decimal values.
Common aspect ratios and example resolutions
| Ratio | Decimal | Common use | Example resolution |
|---|---|---|---|
| 16:9 | 1.78 | HD video, TVs, YouTube | 1920×1080 |
| 4:3 | 1.33 | Classic TV, tablets | 1024×768 |
| 21:9 | 2.33 | Ultrawide monitors, cinema | 2560×1080 |
| 1:1 | 1.00 | Instagram square posts | 1080×1080 |
| 3:2 | 1.50 | DSLR photos, prints | 3000×2000 |
| 9:16 | 0.56 | Reels, Shorts, Stories | 1080×1920 |
| 4:5 | 0.80 | Instagram portrait posts | 1080×1350 |
Frequently asked questions
- What is an aspect ratio?
- An aspect ratio is the proportion of width to height, written as two numbers with a colon such as 16:9. It describes shape, not size, so any image with the same ratio looks proportionally identical regardless of its pixel count.
- What is the aspect ratio of 1920x1080?
- It is 16:9. Dividing both numbers by their greatest common divisor of 120 gives 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9 — the standard widescreen Full HD ratio.
- How do I resize an image keeping the ratio?
- Lock the original ratio, change only one dimension, and compute the other: new height = new width × ratio height ÷ ratio width. That keeps the proportions and avoids stretching.
- What is a 16:9 or 4:3 aspect ratio?
- 16:9 is the modern widescreen ratio used by HD video, monitors and YouTube. 4:3 is the older, more square ratio used by classic TVs and many tablets.
- How do I calculate height from width at a given ratio?
- Multiply the width by the ratio's height value and divide by its width value. At 16:9, a width of 1920 gives 1920 × 9 ÷ 16 = 1080.
- What aspect ratio is best for YouTube or Instagram?
- YouTube videos use 16:9 landscape and Shorts use 9:16 vertical. Instagram feed posts suit 1:1 or 4:5, while Stories and Reels use 9:16.