Image Aspect Ratio Calculator
Work out the ratio behind any pair of dimensions and resize without distortion. Enter a width and height, or read them from an image, to get the simplified ratio, the nearest standard format and matching sizes for any new width or height.
- Files stay on your device
- No sign-up
- Free to use
Your dimensions
Resize with the same ratio
Type a new width or height; the other is calculated to keep the shape.
Shape
Common ratios
Picking a ratio keeps your width and recalculates the height.
How to use Image Aspect Ratio Calculator
- Enter a width and height, or select Read from an image to fill them in from a file.
- Read the simplified ratio, the decimal ratio and the closest common format.
- Under Resize with the same ratio, type a new width or height; the other value is calculated for you.
- Pick a common ratio on the right to see the height it would need at your current width.
Image Aspect Ratio Calculator features
Simplified ratio
Reduces dimensions such as 1920 × 1080 to 16:9 using the greatest common divisor.
Nearest standard
Finds the closest common ratio, such as 3:2 or 4:5, and shows how far off it is.
Proportional resizing
Calculates the matching height for a new width, or width for a new height, rounded to whole pixels.
Live shape preview
A scaled rectangle shows the proportions at a glance.
Read from images
Load an image file to use its real pixel dimensions; the file is not uploaded.
Common ratio presets
Widescreen, photo, portrait print, Instagram, stories and link previews in one click.
When to use Image Aspect Ratio Calculator
- Finding the right height for an image that must be 1200 pixels wide.
- Checking whether a photo matches a 16:9 slide or video frame.
- Planning crop sizes for social media formats.
- Setting width and height attributes for responsive images.
- Converting design dimensions between devices.
Image Aspect Ratio Calculator FAQ
How is the aspect ratio calculated?
The width and height are divided by their greatest common divisor, the largest number that divides both exactly. 1920 and 1080 share 120, giving 16:9.
Why does my ratio look strange, like 683:384?
Some sizes, such as 1366 × 768, do not reduce to small numbers. The calculator therefore also shows the closest standard ratio (16:9 in this case) and the decimal value.
How do I keep proportions when resizing?
Multiply the original height by the new width divided by the original width. The calculator does this for you and rounds to whole pixels, noting any tiny difference caused by rounding.
What does 1.91:1 mean?
A ratio written with a decimal. 1.91:1 is the shape used for link previews on Facebook and LinkedIn, typically 1200 × 628 or 1200 × 630 pixels.
Does the ratio affect image quality?
No. Ratio describes shape only. Quality depends on the number of pixels and compression. Changing the ratio of an existing image requires cropping or adding space, otherwise the picture will be stretched.
A short guide to aspect ratios
Aspect ratio is the relationship between width and height, written as two numbers separated by a colon. It describes shape independently of size: a 16:9 image can be 640 × 360 or 3840 × 2160. Keeping the ratio constant while changing size is what scaling means; changing the ratio means cropping, padding or distorting the picture.
Many familiar ratios come from history and hardware. 4:3 was the shape of early film and television, 3:2 matches the 35 mm film frame still used by most camera sensors, and 16:9 was chosen in the 1980s as a compromise between television and cinema widescreen formats. Phones popularised vertical formats such as 9:16 for full-screen stories and 4:5 for feed posts that take up more screen space than squares.
On the web, declaring an image’s width and height or a CSS aspect-ratio lets the browser reserve the correct space before the image loads. That prevents content from jumping as images appear, which improves both user experience and the Cumulative Layout Shift metric used by search engines to assess page experience.
When an image must change ratio, decide what can be sacrificed. Crop with the Image Cropper when the edges are expendable, add bars or a background with the Image Resizer’s fit option when everything must stay visible, and avoid stretching, which distorts faces and text.