Aspect Ratio Resize Calculator
Type the original width and height, then set either a new width or a new height. The calculator scales the dimension you left alone by the same factor, so the frame keeps its proportions, and it prints the simplified ratio underneath. It works for stills and video, landscape or portrait, and copies the result as WxH plus the ratio.
How to resize keeping the aspect ratio
- Enter the original width and the original height in pixels at the top.
- In the 'Set' menu, choose whether you will type a New width or a New height.
- Type the target value in the field that stays enabled; the other field fills in automatically.
- Read the New size and the Aspect ratio in the highlighted box below.
- Click Copy to grab the result as, for example, 1280x720 (16:9).
Examples
Scale a 1080p frame down to 1280 wide
Original 1920x1080, Set New width, New width 1280
1280 x 720, aspect ratio 16:9
Solve the width from a target height of 480
Original 1920x1080, Set New height, New height 480
853 x 480, aspect ratio 16:9
Shrink a portrait phone clip
Original 1080x1920, Set New width, New width 720
720 x 1280, aspect ratio 9:16
Frequently asked questions
How does proportional resizing work here?
The engine scales the dimension you did not set by the same factor as the one you did. If you set a new width, the height becomes new width times original height divided by original width; if you set a new height, the width becomes new height times original width divided by original height. Both results are rounded to whole pixels.
Why does the ratio sometimes drift by a hair?
Screens can only show whole pixels, so a scaled value like 853.33 is rounded to 853. That rounding can nudge the true ratio by a fraction of a percent, but it guarantees the output is a valid integer size no video encoder or image editor will reject.
How is the simplified aspect ratio found?
It divides the original width and height by their greatest common divisor. For 1920 by 1080 the divisor is 120, which reduces to 16:9. For 1080 by 1920 the same divisor gives 9:16. The ratio is always taken from the original dimensions, not the resized ones.
Can I use this for portrait or square sources?
Yes. A taller-than-wide source such as 1080 by 1920 returns 9:16, and a 1000 by 1000 source returns 1:1. The formula does not care which dimension is larger, so any orientation resizes correctly.
Does it actually resize my image or video file?
No. This is a math tool that gives you the exact pixel dimensions to plug into your editor, encoder or CSS. Take the numbers into a program like Photoshop, GIMP, HandBrake or ffmpeg to perform the real resize.
Will resizing stretch or distort the picture?
Not when you use these numbers. Because both dimensions change by the same factor, the shape is preserved and nothing looks squashed or stretched. Distortion only happens if you override one value by hand to break the ratio.
What inputs are rejected?
Every field must be a number greater than zero. A blank, zero or negative width or height shows a short prompt instead of a result, and you can only set one of the two new dimensions at a time.
Does it handle non-standard ratios like 21:9 or 4:3?
Yes. The tool reads whatever ratio your original dimensions imply, so an ultrawide 2560 by 1080 source reports 64:27 and a classic 640 by 480 source reports 4:3. There is no fixed list of ratios.
Is anything uploaded when I use this?
No. The calculation runs entirely in your browser with plain arithmetic, so the dimensions you type never leave your device and nothing is stored.
Learn more
- Common Video Resolutions and Aspect Ratios
A reference for the standard pixel sizes behind 16:9, 9:16, 4:3 and ultrawide, and how to scale between them without distortion.
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