Aspect Ratio Calculator
Resize images and video without distortion. Enter your original size, change the width or height, and the other side is worked out for you — plus the simplified ratio.
Common ratios
New size — fill in ONE, the other follows
What Is an Aspect Ratio?
An aspect ratio is the relationship between width and height, written as width:height. A 1920×1080 image is 16:9 because both numbers divide down to 16 and 9. The ratio describes the shape, not the size — 1920×1080 and 1280×720 are different sizes with identical shape.
Keeping the ratio constant when you resize is what stops images looking stretched or squashed. To halve the width of a 16:9 image you must halve the height too.
Common Aspect Ratios and Where They Are Used
- 16:9 — the standard for video: YouTube, TVs, monitors, presentation slides. 1920×1080 and 3840×2160 are both 16:9.
- 9:16 — vertical video for TikTok, Reels, Shorts and Stories. Usually 1080×1920.
- 1:1 — square, used for profile pictures, avatars and Instagram feed posts.
- 4:3 — older monitors, many tablets, and most compact-camera photos.
- 3:2 — the classic 35mm film shape, still used by most DSLR and mirrorless sensors, and it matches 6×4 prints.
- 21:9 — ultrawide monitors and cinematic video.
Resizing Without Distortion
The maths is a simple proportion: new height = new width × (original height ÷ original width). For a 1920×1080 image resized to 1280 wide, the height is 1280 × (1080 ÷ 1920) = 720.
Results are rounded to whole pixels, so occasionally a resized dimension is off by one from the perfect ratio — pixels cannot be fractional. That single pixel is never visible, but it is why 1367×769 can appear instead of an exact 16:9.
Changing the Ratio: Crop, Don’t Stretch
If you need a 16:9 photo to become square, you cannot just change the numbers — that stretches faces and objects and looks instantly wrong. Instead crop to the new shape, discarding what falls outside, or add letterbox bars to pad it. Use the Image Cropper for that, then come back here to scale the cropped result.
Frequently Asked Questions
Is 1080p the same as 16:9?
1080p means 1080 pixels tall. Paired with 1920 wide that is 16:9, which is the usual case, but the number alone describes height rather than shape.
Why is my resized image one pixel off?
Because pixels must be whole numbers. When the exact result is fractional it is rounded, which can leave a dimension one pixel from the perfect ratio. It is never visible.
Does resizing reduce quality?
Making an image smaller is generally safe. Making it larger cannot invent detail that was not captured, so enlarged images look soft. Always scale down from the largest original you have.
What ratio should I use for social media?
Use 1:1 or 4:5 for Instagram feed posts, 9:16 for Stories, Reels, Shorts and TikTok, and 16:9 for YouTube thumbnails and video.