Aspect Ratio Calculator

Resize an image to a new width or height while preserving the original aspect ratio — with preset 16:9, 4:3, 1:1, 21:9.

Result

Loading calculator…

—

How to use this calculator

Enter the original width and height — usually from the file properties or an image viewer.
Pick the mode that matches what you know: target width, target height, or a preset crop.
Read the new dimensions and apply them in your image editor (Photoshop / GIMP / Squoosh / ImageMagick).

About this calculator

Image-resize math, in one tool. Aspect ratio = width / height. If you change just the width, you have to change the height by the same proportion (width / ratio) — otherwise the image gets distorted. The calculator handles three common workflows: (1) "I have a new width, what height keeps the ratio?", (2) "I have a new height, what width?", and (3) "Crop to a preset ratio at a given long-edge size". The preset list covers the dominant industry standards — 16:9 for video, 1:1 for Instagram, 9:16 for phone-vertical, 3:2 for DSLR photos, 21:9 for ultrawide cinema. The "simplified ratio" line uses the greatest common divisor to reduce 1920×1080 to its iconic 16:9 form.

Frequently asked

Why does my resized image look stretched?+

You probably changed width and height independently without preserving the ratio. The fix is to set EITHER width OR height in the new image, and let the other dimension scale automatically (this tool computes it).

What is the difference between 16:9 and 16/9?+

Same thing. 16:9 is the ratio notation, 16/9 ≈ 1.7778 is the decimal. Both mean: width is 1.7778× the height.

What is the smallest "lossless" image size?+

There isn't one in the strict sense — any pixel resize involves interpolation. Using exact integer multiples (½, ⅓, ¼ of original) minimises blur because pixels map cleanly without averaging.

When do I need a preset crop?+

When the target platform demands a specific ratio (Instagram = 1:1; TikTok = 9:16; YouTube = 16:9) and your source ratio is different. You either letterbox (add bars) or crop to fit.

Source for the preset ratios?+

SMPTE / ITU-R BT.709 (16:9 HD), Academy of Motion Picture Arts and Sciences (21:9 cinemascope), Instagram Help Center (1:1, 4:5, 9:16), and traditional 35 mm photography conventions (3:2 landscape, 2:3 portrait).