Quick start
- Use Simplify ratio when you only need the width-to-height relationship, such as 3840 x 2160 becoming 16:9.
- Use Scale by width when you know the new width and need the matching height, such as a 1080 x 1920 story resized to 720 wide.
- Use Scale by height when you know the new height and need the matching width.
- Keep width and height in the same unit. Pixels, inches, and centimeters can all work, but do not mix them in the same calculation.
Best uses
Use this guide when you already know the original dimensions and need a clean resize, simplified ratio, or quick check before exporting an image, video, screenshot, or thumbnail.
- Simplify image, video, thumbnail, and screenshot dimensions.
- Resize a design to a new width while preserving height proportion.
- Resize a design to a new height while preserving width proportion.
- Compare landscape, square, and portrait formats before exporting.
What this calculator is solving
The Aspect Ratio Calculator keeps designs, screenshots, images, thumbnails, and video frames from stretching when one dimension changes.
Match each input label on the calculator to the original width and height, using the same unit, plus either the new width or the new height when you are resizing.
The formula in plain language
In plain language: The calculator scales decimal inputs to whole-number precision, divides width and height by their greatest common divisor to simplify the ratio, then uses width / height to calculate the missing scaled dimension. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
For example, 3840 x 2160 simplifies to 16:9 because both numbers divide down to 16 and 9. If a 1080 x 1920 vertical story needs to become 720 pixels wide, the matching height is 1280 pixels, so the file keeps the same shape.
How to read the answer
Read the simplified ratio first, then check the decimal and scaled-size lines. If the answer is for an upload, design system, or video editor, compare the final rounded pixels with that platform before exporting.
- Ratio shows the simplified width-to-height relationship, such as 16:9, 1:1, or 4:5.
- Decimal shows width divided by height, which helps compare two sizes that may not look obviously related.
- Scaled size shows the missing dimension when you resize by width or height.
- A one-pixel difference can happen after rounding when the exact scaled answer is a decimal pixel.
Common mistakes to avoid
Most aspect-ratio mistakes come from mixing units, rounding too early, or resizing when the real job needs a crop or padded canvas.
- Do not round too early when a platform needs exact pixels.
- Do not crop and resize as if they are the same thing; cropping changes what is visible.
- Do not assume a ratio tells you which part of the image should stay in frame.
- Check the final export dimensions after compression, image editing, or video rendering.
One vertical story example
Say a vertical design is 1080 x 1920 and you need a smaller copy that is 720 pixels wide. Choose Scale by width, enter 1080 as the original width, 1920 as the original height, and 720 as the new width.
The calculator returns 720 x 1280. That means the image is smaller, but it has not been squashed or stretched. If the destination requires a different shape, resize alone is not enough.
- 1080 x 1920 simplifies to 9:16.
- 720 / 1080 = 0.666666..., so the height scales by the same factor.
- 1920 x 0.666666... = 1280.
Resize, crop, or pad?
Resizing keeps the whole image and changes its size. Cropping cuts away part of the image to fit a different shape. Padding keeps the whole image but adds empty space around it.
If your 1200 x 630 social preview needs to stay the same shape at 600 pixels wide, resizing gives 600 x 315. If a platform asks for a square, you need a crop or padded canvas instead of only a scaled size.
- Resize when the shape can stay the same.
- Crop when the destination shape is different and losing edges is acceptable.
- Pad when the destination shape is different but the whole image must stay visible.
Research and references
These references help check the aspect-ratio concept and same-unit measurement context behind the guide examples.
Worked examples for Aspect Ratio Calculator
16:9, decimal 1.7777777778
720 x 1280
600 x 315
FAQ in plain language
When should I use the Aspect Ratio Calculator?
Use it when your task matches one of these common needs: Simplify image, video, thumbnail, and screenshot dimensions. Resize a design to a new width while preserving height proportion. It works best when you already know the original width and height, plus either the new width or the new height when you are resizing.
What is the Aspect Ratio Calculator doing with my inputs?
In plain language: The calculator scales decimal inputs to whole-number precision, divides width and height by their greatest common divisor to simplify the ratio, then uses width / height to calculate the missing scaled dimension. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
What do the main Aspect Ratio Calculator inputs mean?
Width: the horizontal size of the image, video, screen, card, or design. Height: the vertical size of the same item, using the same unit as width. Simplified ratio: the width and height divided by their greatest common divisor, such as 1920 x 1080 becoming 16:9. Decimal: width divided by height, useful for comparing whether two sizes have the same shape. Scaled size: the matching width or height that keeps the original shape when one dimension changes.
How should I read the Aspect Ratio Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the answer?
Aspect ratio preserves shape, not subject framing. Use exact upload specs for platforms, product images, video editors, and print jobs, and remember that rounding a scaled dimension can cause a one-pixel difference. Check whether the job needs resizing, cropping, padding, or a platform-specific preset because keeping the same ratio does not decide what part of the image stays visible.
What is an aspect ratio?
An aspect ratio is the relationship between width and height. A 16:9 image can be 1920 x 1080, 1280 x 720, or 3840 x 2160 because each size keeps the same width-to-height shape.
How do I scale a 16:9 video to 1280 wide?
Enter 1920 width, 1080 height, choose Scale by width, and enter 1280 as the new width. The matching height is 720, so the scaled size is 1280 x 720.
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Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
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Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.