Aspect ratio describes the relationship between an image or video frame's width and height. It helps you choose a frame that fits a screen, social feed, website component, or print layout without stretching the subject. For a fast calculation, open the aspect ratio calculator, enter the width and height, and copy the simplified ratio.
What is aspect ratio?
Aspect ratio is written as width:height. A 16:9 frame is wider than it is tall, while 9:16 is the vertical version of the same relationship. A 1:1 frame has equal width and height, so it is square.
The ratio is independent of the absolute pixel dimensions. 1920×1080, 1280×720, and 640×360 are all 16:9. They have different resolutions, but the same shape.
How to calculate aspect ratio from width and height
1. Write the dimensions as width:height
Start with the actual pixel dimensions. For a 1920×1080 image, write 1920:1080. Keep the order consistent: width first, height second.
2. Find the greatest common divisor
Divide both numbers by their greatest common divisor. For 1920 and 1080, the greatest common divisor is 120:
1920 ÷ 120 = 16
1080 ÷ 120 = 9
The simplified aspect ratio is 16:9. You can use the aspect ratio calculator to do this reduction automatically and show the total pixels and megapixels as well.
3. Compare the result with the destination
Once you know the ratio, compare it with the platform or layout that will display the asset. If the shapes differ, decide whether to crop, letterbox, or reframe the source. Stretching the width and height independently changes the subject's proportions.
Common image and video aspect ratios
- 16:9: landscape video, presentations, and many web players.
- 9:16: vertical video for stories, Shorts, Reels, and full-screen mobile feeds.
- 1:1: square avatars, product cards, and square social posts.
- 4:3: classic displays, some presentations, and older camera formats.
- 3:4: portrait-oriented layouts and some photo cards.
- 21:9: wide cinematic frames and banner-style compositions.
These are starting points rather than permanent platform rules. Check the current destination specification when the exact ratio, safe area, or pixel size matters.
How to find a missing dimension from an aspect ratio
If you know the ratio and one side, multiply or divide using the ratio parts. For a 16:9 frame that is 1280 pixels wide:
height = 1280 × 9 ÷ 16 = 720
The matching frame is 1280×720. For a 9:16 vertical frame that is 1080 pixels wide:
height = 1080 × 16 ÷ 9 = 1920
The aspect ratio calculator has a ratio mode for this direction: choose a common ratio or enter a custom one, then provide one dimension to get the other.
Aspect ratio versus resolution
Aspect ratio is shape; resolution is the number of pixels. Two videos can share 16:9 but have different sharpness and file sizes because one might be 3840×2160 and the other 1280×720. Choose the ratio to fit the frame, then choose the resolution for the intended display size and delivery budget.
If the source has the wrong shape, use the image cropper or video cropper to reframe it. If the shape is already correct but the dimensions are too large, use the image resizer or video resizer without unlocking the aspect ratio.
Common aspect ratio problems
The video looks stretched
The width and height were likely changed independently. Restore the original ratio or crop to the destination shape. Do not use a resizer with the aspect-ratio lock disabled unless you deliberately want a distorted result.
The frame has black bars
Black bars usually mean the source and player shapes do not match. Crop or reframe when filling the destination is more important than preserving the complete source. Use letterboxing when keeping the entire frame is more important.
The calculated ratio is not a familiar number
The source may have a custom ratio, non-square pixels, or dimensions that do not reduce to a common preset. Keep the exact simplified ratio for planning, and verify how the destination interprets the file.
FAQ
How do I calculate aspect ratio?
Write the width and height as a ratio, then divide both by their greatest common divisor. For 1920×1080, divide both by 120 to get 16:9. The aspect ratio calculator automates the calculation.
What aspect ratio is 1920×1080?
1920×1080 is 16:9. 1280×720 and 640×360 have the same aspect ratio at smaller resolutions.
How do I calculate the height for a 16:9 video?
Multiply the known width by 9 and divide by 16. For a 1280-pixel width, the height is 720 pixels.
Should I crop or resize to change aspect ratio?
Crop when the composition needs a new shape and resize when the shape is already correct but the pixel dimensions are too large. Cropping preserves proportions; independent resizing can stretch the subject.
Does aspect ratio affect video quality?
The ratio describes shape, not quality. Quality also depends on resolution, bitrate, codec, source detail, and the display size.
Continue to the calculator tools
Use the aspect ratio calculator to reduce dimensions or find a missing side, then use the appropriate video cropper or image cropper when the source frame needs a new composition.