Aspect Ratio Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
To resize an image without distorting it, keep the same width/height ratio: target height = original height × (target width ÷ original width). A 1920×1080 image reduced to a width of 1280 gives a height of 720.
Explanation
The aspect ratio of an image or video is the proportion between its width and its height (for example 16:9 for a widescreen video, or 4:3 for a more square format). Resizing an image by changing only one dimension (for example only the width, in an editing program or a CSS stylesheet) without recalculating the other proportionally stretches or squashes it visually. This calculator applies a simple rule of three to find the missing dimension: it multiplies the original height by the scale factor applied to the width (target width ÷ original width), exactly the same mathematical principle as a classic rule of three. A common 16:9 format (like 1920×1080) resized to a width of 1280 will always give a height of 720, regardless of the starting point, as long as the 16:9 ratio is preserved. For a more general proportion calculation (not limited to image dimensions), see our rule of three calculator.
Example: reducing a 1920×1080 image to a width of 1280
Inputs
Original width: 1920 px. Original height: 1080 px. Target width: 1280 px.
Calculation
Scale factor = 1280 ÷ 1920 = 0.6667. Target height = 1080 × 0.6667 = 720.
Result
The new height, to keep the proportions, is 720 px.
Frequently asked questions
What happens if I don't respect the original aspect ratio?
The image or video appears stretched horizontally or vertically (distorted), with circles becoming ovals and faces looking wider or longer than reality. This is a common mistake when resizing only one dimension in an image editor without locking the proportions.
How do I calculate the width from a new height instead?
Use the same logic in reverse: target width = original width × (target height ÷ original height). This calculator is set up for the most frequent use case (finding the height from a new width), but the proportionality principle stays the same in both directions.
What are the most common aspect ratios?
16:9 is the standard for video and modern screens (e.g., 1920×1080, 1280×720). 4:3 was the standard for older screens and film photography. 1:1 (square) and 9:16 (vertical format) are common on social media. This calculator works with any starting dimensions, not just these standard formats.