Aspect Ratio

How Aspect Ratio Is Calculated

An aspect ratio describes the shape of an image, video, or screen as the ratio between its width and height. Enter your original width and height, along with the new width or height you want, and this calculator finds the matching dimension that keeps the same shape.

Key Factors to Consider

• A resized dimension may not land on a whole pixel. Since real screens and image files use whole pixels, a calculated dimension with a fraction (like 450.6px) typically needs to be rounded — rounding up avoids cropping content, while rounding down avoids stretching, so pick based on which tradeoff matters more for your use case.
• Common video and screen aspect ratios have their own standard names. 16:9 is the standard widescreen ratio for most modern video and displays, 4:3 was the standard for older television and computer monitors, and 21:9 (or similar) describes an ultrawide display — knowing which standard ratio your target dimensions simplify to can help when choosing export or crop presets.
• Cropping and resizing are different operations that both affect aspect ratio. Resizing keeps the same visual content and just scales it, while cropping removes part of the image to force it into a specific ratio — if you need to fit content into a specific ratio without distortion, cropping (not stretching) is usually the right tool.
• Some platforms enforce specific aspect ratios regardless of your source file. Many social media platforms crop or letterbox uploaded images/videos to fit their own preferred ratios — check your target platform’s requirements before assuming your calculated dimensions will display exactly as intended.

Common Mistakes

• Swapping width and height. Entering height where the calculator expects width (or vice versa) produces a technically-correct-looking but wrong result — double-check which dimension you’re resizing before reading the answer.
• Rounding the original ratio before calculating. Simplifying 1920x1080 to “16:9” and then calculating from the rounded ratio instead of the exact original pixel dimensions can introduce a small but avoidable error — use the exact original dimensions whenever you have them.
• Assuming every platform will display your resized content at exactly that ratio. Some platforms crop, letterbox, or pad content that doesn’t match one of their own preferred ratios, even if your math is perfectly correct.

The Formula

$$\vB{\text{New Height}} = \vC{\text{New Width}} \times \frac{\vA{\text{Original Height}}}{\vA{\text{Original Width}}}$$

or, solved for width: new width = new height × (original width ÷ original height).

Worked Example

A 1920x1080 image resized to a width of 800:

1. $\vB{\text{New Height}} = \vC{800} \times \frac{\vA{1080}}{\vA{1920}} = \vB{450}$ px.

Useful to Know

A file’s pixel dimensions don’t always match its displayed aspect ratio, because of pixel aspect ratio (PAR). Some video formats — particularly older broadcast and DVD/anamorphic formats — store non-square pixels, so a file’s raw width-to-height pixel count isn’t the same ratio the footage is meant to be displayed at. This calculator works from the pixel dimensions you enter, which matches modern web images, photos, and most video; for anamorphic or broadcast-legacy footage specifically, check the format’s intended display ratio rather than assuming the stored pixel dimensions tell the whole story.