Aspect ratio calculator
Simplify a ratio, or find the missing side.
Scale to a new size
Type a new width or height and the other side updates to keep the same ratio.
- Common presets included
- Finds the missing width or height
- Always simplified
How to calculate an aspect ratio
- Enter a width and height, or pick a preset.
- Read the simplified ratio.
- Type a new width or height to scale proportionally.
Common ratios and where they are used
| Ratio | Example resolution | Used for |
|---|---|---|
| 16:9 | 1920x1080, 3840x2160 | HD and 4K video, most laptop and TV screens |
| 4:3 | 1024x768 | Older TVs and monitors, standard printed photos |
| 21:9 | 2560x1080, 3440x1440 | Ultrawide monitors and cinematic video |
| 9:16 | 1080x1920 | Phone screens, Reels, Stories and TikTok |
| 1:1 | 1080x1080 | Square social posts, the original Instagram format |
Worked examples
- 3840x2160 (4K) simplifies to 16:9, the exact same ratio as 1920x1080 and 1280x720, just at a higher pixel count.
- A 4x6 inch print simplifies to 2:3, while an 8x10 inch print simplifies to 4:5, a different shape, so an 8x10 print of a 4x6 photo always crops some of the edges.
- A 2560x1080 ultrawide monitor actually simplifies to 64:27, not a perfect 21:9. Marketed "21:9" ultrawide resolutions are all close approximations, since no whole-pixel resolution hits 21:9 exactly.
- A photo cropped to an odd size like 1920x1005 has no common name. Both numbers share a greatest common factor of 15, so dividing each by 15 simplifies it to 128:67, a real ratio, just not one anybody names.
Scaling by width vs height
Typing a new width keeps the ratio and solves for the matching height, which is the right move when you know how wide a slot needs to be, like a website banner. Typing a new height does the reverse.
Say a 2560x1440 monitor screenshot needs to shrink to 1024 pixels wide for a blog post. The new height is 1024 x 1440 / 2560 = 576, so it lands at 1024x576, still 16:9.
Scaling like this stretches nothing: every pixel keeps its place relative to the others. If you need a different shape entirely, such as fitting a 16:9 video into a 1:1 square post, that calls for cropping, not scaling, since no resize can change the ratio itself.
Aspect ratio calculator FAQ
What ratio is 1920 by 1080?
16:9, the standard widescreen ratio for HD and 4K video.
If I resize 1920x1080 to a width of 1280, what is the height?
720, since 1280 is two thirds of 1920 and the same scale keeps the 16:9 ratio, giving 1280x720.
What is 4:3 used for?
4:3 was the standard ratio for older televisions and monitors, and is still used for some presentation slides and printed photos.
What is 9:16 used for?
9:16 is the vertical ratio used by phone screens and short-form video like Reels and Stories, the rotated version of 16:9.
Why is my ratio not a clean number?
Odd pixel dimensions do not always reduce to a common named ratio. The tool still shows the fully simplified fraction, even if it looks unfamiliar.
Is an 8x10 print the same ratio as a 4x6?
No. 4x6 simplifies to 2:3, while 8x10 simplifies to 4:5, a squarer shape. Printing a 4x6-ratio photo at 8x10 crops part of the image to fit.
Is a "21:9" ultrawide monitor really 21:9?
Not exactly. A common ultrawide resolution like 2560x1080 simplifies to 64:27, not 21:9. True 21:9 would need a fractional pixel count, so "21:9" is a rounded marketing name for a group of close ratios.
What ratio is a 4K screen?
3840x2160 simplifies to 16:9, the same ratio as 1080p (1920x1080) and 720p (1280x720). 4K is a higher resolution at the same shape, not a wider one.