Aspect Ratio Calculator (Resize & Crop)
Enter a width and height and this calculator reduces them to a clean aspect ratio like 16:9 or 4:3, tells you whether it's a recognised standard, and solves the matching height for any new width you want to resize to. It's the quick tool for resizing images and video without stretching or distortion.
Original size (px)
Aspect ratio
16:9
Widescreen (16:9) · 1.78:1
Resized keeping ratio
1,280 × 720 px
Compare scenarios
Run the same calculation with two or three input sets side by side. Differences are highlighted; every number comes from the same tested formula as the calculator above.
| Input | Scenario A | Scenario B |
|---|---|---|
| Width | ||
| Height | ||
| New Width |
How it works
An aspect ratio is the proportional relationship between width and height, written as two numbers like 16:9. To simplify raw pixel dimensions to that form, the calculator divides both by their greatest common divisor (GCD). 1920 and 1080 share a GCD of 120, so 1920:1080 reduces to 16:9 — the same shape, expressed in the smallest whole numbers.
To resize without distortion, the ratio must stay constant. Given a new width, the matching height is newWidth × (originalHeight ÷ originalWidth). Resizing a 1920×1080 image to 1280 wide gives 1280 × (1080/1920) = 720 tall, preserving 16:9. Change only one dimension freely and you stretch the image; solve the other with this ratio and it stays proportional.
The calculator also flags common ratios — 16:9 widescreen, 4:3 standard, 3:2 for most cameras, 1:1 square, 21:9 ultrawide, and the vertical/portrait variants used on social platforms. Knowing the named ratio helps you match delivery specs: a video timeline expects 16:9, a phone story wants 9:16, and a print may need 3:2 or 4:5. If your dimensions don't reduce to a familiar ratio, that's a sign you may need to crop to hit a target format.
Frequently asked questions
What's the difference between resizing and cropping?+
Resizing scales the whole image up or down while keeping its aspect ratio, so nothing is cut off and nothing is distorted — this calculator's 'solve the new height' function does exactly that. Cropping changes the aspect ratio by cutting away part of the image to fit a different shape, which loses content but lets you convert, say, a 3:2 photo to a 1:1 square. If your source ratio doesn't match your target, you crop first (changing the pixel dimensions), then resize the cropped result to the final size.
Why does my image look stretched after resizing?+
Because you changed width and height by different proportions, breaking the aspect ratio. If you set a new width but pick a height that isn't the ratio-preserving value, the image squashes or stretches. The fix is to change only one dimension and let the other be calculated from the original ratio — which is what this tool does. Most image editors have a 'constrain proportions' or 'lock ratio' toggle that enforces the same math automatically.
What are the most common aspect ratios I should know?+
16:9 is the standard for video, TVs, and most monitors. 4:3 is older standard-definition and many tablets. 3:2 is the native ratio of most DSLR and mirrorless cameras (and 35mm film). 1:1 is square, popular for social feeds. 9:16 is vertical for phone stories and short-form video, and 4:5 is the tall portrait ratio that performs well in social feeds. Matching your export to the platform's expected ratio avoids automatic cropping or letterboxing that can cut off important parts of your image.