How to calculate an aspect ratio
- Enter a width and height to see their simplified ratio, such as 1920 × 1080 → 16:9.
- Or pick a ratio, either a preset or your own, and enter one dimension.
- Read the missing width or height, rounded to whole pixels.
- Crop or resize your image to match with Crop Image.
How aspect ratios are calculated
An aspect ratio is width and height divided by their greatest common divisor. For 1920 × 1080 that divisor is 120, giving 16:9. Some common sizes don't simplify neatly: 1366 × 768 reduces to 683:384, which is very close to 16:9, so the calculator also shows the decimal ratio to help you compare.
Common ratios and where they're used
- 16:9: widescreen video, YouTube, TVs and most monitors.
- 9:16: vertical video such as Stories, Reels and Shorts.
- 4:3: older displays, many tablets and phone camera photos.
- 3:2: most DSLR and mirrorless camera photos, 4 × 6 inch prints.
- 1:1: square posts and profile pictures.
- 4:5: portrait-oriented social media posts.
- 21:9: ultrawide monitors and cinematic video.
Finding a missing dimension
If you know the ratio a:b and the width, the height is width × b ÷ a. A 1280-pixel-wide video at 16:9 is therefore 720 pixels tall. For pixel and print-size conversions at a given DPI, use the Image Dimension Calculator. In the other direction, a 1920-pixel-tall vertical video at 9:16 is 1080 pixels wide. Sizes that do not divide evenly are rounded to the nearest whole pixel.
Frequently asked questions
What resolutions are 16:9?
Common ones include 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160.
Is 1366 × 768 exactly 16:9?
Not exactly. It simplifies to 683:384, which is very close to 16:9 (1.779 versus 1.778).
How do I make an image a specific ratio?
Crop it to the ratio with Crop Image, then resize it to the exact pixel dimensions you need.
Do I need to upload anything?
No. The calculator works with the numbers you type.