What is Aspect Ratio Calculator?
Free aspect ratio calculator. Enter width and height to get the simplified ratio, or lock any dimension and scale to any size. Works for images, videos, and screens. No signup.
Aspect Ratio runs entirely in your browser using JavaScript (browser). Your data never leaves your device.
Free Aspect Ratio Calculator
Calculate the aspect ratio of any image, video, or screen size — and scale dimensions while maintaining it. Enter width and height to see the simplified ratio (e.g., 1920×1080 → 16:9). Or enter a known ratio and one dimension to calculate the missing dimension. Supports all common ratios: 16:9, 4:3, 1:1, 21:9, and custom values. Useful for resizing images, designing video thumbnails, setting viewport dimensions, and cropping photos.
Enter Dimensions
Aspect Ratio
16:9
Common Aspect Ratios
Scale to New Size
Enter one dimension — the other is calculated automatically to maintain 16:9.
All calculations run in your browser. No data is sent to any server.
Frequently Asked Questions
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Understanding Aspect Ratios
An aspect ratio describes the proportional relationship between the width and height of a rectangle. It is written as two whole numbers separated by a colon — for example, 16:9 means the image is 16 units wide for every 9 units tall. The same ratio applies at any resolution: 1280×720, 1920×1080, and 3840×2160 are all 16:9. The numbers are always reduced to their smallest whole-number form by dividing by the greatest common divisor (GCD).
Common Aspect Ratios and Their Uses
16:9 is the standard widescreen ratio for HD and 4K video, YouTube, most monitors, and laptops. 4:3 was the standard for older CRT televisions, many tablets (including older iPads), and is still common in presentation software. 1:1 (square) is used for Instagram feed posts, album covers, and profile photos. 9:16 (vertical widescreen) is used for Instagram Stories, TikTok, YouTube Shorts, and Snapchat. 21:9 (ultrawide) appears in cinematic content and ultrawide monitors. 3:2 is common in DSLR photography (APS-C and full-frame sensors) and is the basis for standard print sizes like 4×6 and 6×9 inches.
Maintaining Aspect Ratio When Resizing
To resize an image without distortion, you must maintain the original ratio. Multiply both width and height by the same scale factor, or use this calculator's Scale panel — enter the new width and the correct height is calculated automatically. In CSS, setting aspect-ratio: 16 / 9 on an element maintains the ratio as the element resizes. In image editors like Photoshop and GIMP, the lock icon next to the dimensions preserves the ratio automatically.