Calculators
Aspect Ratio Calculator
Work out the simplified ratio of any pixel dimensions, or find the missing width or height when scaling an image so its proportions stay exactly the same.
It is the fastest way to answer questions such as "if this 1920 × 1080 banner has to be 1280 pixels wide, how tall should it be?"
Mode 1 — Calculate the ratio
Enter any width and height in pixels to see the simplified ratio.
Aspect ratio
16:9
Decimal ratio
1.7778
Greatest common divisor
120
Mode 2 — Solve a missing dimension
Enter the original size, then type either a new width or a new height. The other value is calculated so the ratio stays intact.
1920×1080 (16:9) scaled to 1280×720 — calculated from the new width.
How to use this tool
- 1Use Mode 1 to enter a width and height and read the simplified ratio.
- 2Click a ratio preset to see example dimensions for that shape.
- 3Use Mode 2 to enter your original dimensions.
- 4Type either the new width or the new height — the other value is filled in for you.
What is aspect ratio?
Aspect ratio describes the relationship between an image's width and its height, written as two numbers separated by a colon. A 16:9 image is sixteen units wide for every nine units tall, whatever its actual pixel count. Because it is a proportion rather than a measurement, the same ratio describes a thumbnail and a cinema screen equally well.
How aspect ratio is calculated
Take the width and the height, find their greatest common divisor, and divide both by it. For 1600 × 1200 the greatest common divisor is 400, giving 4:3. Dividing width by height also gives a decimal ratio — 1.333 in that example — which is handy when a specification is expressed as a single number such as 1.91:1 for social link previews.
Common social and display ratios
| Ratio | Example resolution | Where it is used |
|---|---|---|
| 1:1 | 1080 × 1080 | Instagram feed posts, avatars, product tiles |
| 4:5 | 1080 × 1350 | Portrait social posts |
| 9:16 | 1080 × 1920 | Stories, Reels, TikTok, vertical video |
| 16:9 | 1920 × 1080 | YouTube, presentations, most monitors and TVs |
| 21:9 | 2560 × 1080 | Ultrawide monitors, cinematic crops |
| 3:2 | 3000 × 2000 | DSLR and mirrorless sensors, 6×4 inch prints |
| 4:3 | 1600 × 1200 | Compact cameras, older displays, tablets |
Resolution versus aspect ratio
Confusing the two causes most layout accidents. Resolution tells you how much detail an image contains and how large it can be displayed before it looks soft. Aspect ratio tells you what shape it is. A container expecting 16:9 will letterbox or crop a 4:3 image regardless of how many pixels that image has. When a design calls for a specific shape, crop with the image cropper first and only then scale with the resizer.
Worked example
A photograph is 4032 × 3024 (4:3) and must fill a 16:9 hero slot 1600 pixels wide. The slot height is 1600 × 9 ÷ 16 = 900 pixels. Resizing alone would squash the picture, so the correct sequence is: crop the original to 16:9, which for a 4032 pixel width means keeping 2268 pixels of height, then resize the crop to 1600 × 900.
Frequently Asked Questions
How is an aspect ratio calculated?
Divide the width and the height by their greatest common divisor. For 1920 × 1080 the divisor is 120, which gives 16:9.
What is the difference between resolution and aspect ratio?
Resolution is the actual pixel count, such as 1280 × 720. Aspect ratio is the shape those pixels form — 1280 × 720 and 1920 × 1080 are different resolutions with the same 16:9 ratio.
Why do some ratios show odd numbers like 683:384?
Because the two dimensions share no convenient divisor. That usually means the image was cropped by hand and is very slightly off a standard ratio.
Which ratio should I use for social media?
1:1 or 4:5 for feed posts, 9:16 for stories and short video, 16:9 for YouTube thumbnails, and roughly 1.91:1 (1200 × 630) for link previews.
Does changing the ratio change the file size?
Indirectly. The ratio itself has no weight, but reaching a new ratio means cropping or resizing, which changes the pixel count and therefore the file size.