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Aspect Ratio Calculator

Enter your original size, then a new width or height — the other side is calculated for you.

Processed entirely in your browser. Never uploaded to a server.

Original size

New size

This tool calculates the missing dimension when you resize an image, so the result keeps the exact proportions of the original. Enter your original width and height, then a new width (or height) — the matching dimension and the simplified ratio (like 16:9 or 4:3) are calculated as you type.

What aspect ratio is, and why distortion happens

Aspect ratio is the relationship between an image's width and height, expressed as a ratio like 16:9 or 4:3. Any resize that keeps that same proportion looks like a clean scaled copy, at any size. Distortion — a stretched or squashed look, circles turned into ovals — happens when a new width and new height are set independently and the two numbers don't match that original relationship, forcing the pixels to spread across a shape they weren't captured for. The fix is always the same formula: pick one dimension, and calculate the other as original × (new ÷ original) rather than typing both in by guess.

FAQ

How does this calculate the missing dimension?
It scales proportionally: new height = original height × (new width ÷ original width), or the same formula solved for width. That single ratio is what keeps a resized image looking like a clean scaled copy instead of a stretched or squashed one.
What does the simplified ratio like "16:9" actually mean?
It is the width-to-height relationship reduced to its smallest whole numbers using the greatest common divisor — a 1920×1080 image and a 320×180 image are both 16:9, because they scale down to the same two numbers.
Why did my resized image come out stretched even though I used a resize tool?
Most likely the tool let you type a width and a height independently, and the two numbers you entered did not match the original ratio. Locking one field to this calculator's output, or using a resize tool that only exposes one dimension, prevents that.
Does this resize my actual image file?
No — this is a calculator only, it works out the numbers. Once you have the target width and height, use Resize Image to actually process the file.
Can I use this for video or print sizes too?
Yes, the ratio math is identical for any width/height pair — video frames, print dimensions, browser windows. It is not specific to photo files.

Want the full explanation, including why some tools distort images by default? Read How to resize an image without distorting its aspect ratio. Once you have your target dimensions, use Resize Image to actually process the file.

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