Aspect ratio calculator
Find the exact ratio and calculate proportional dimensions.
Optional. Leave empty to calculate only the ratio.
Enter a width and height to see the ratio.
Whole numbers: 1–1,000,000. This calculates dimensions; it does not edit images.
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Work out an image or video’s proportions before changing its size. Enter the original width and height to reduce them to an exact ratio, then provide a new width or height to calculate the other side. This is useful when preparing a banner, a video frame or a responsive layout. Nothing is uploaded: the calculator works with numbers, not image files. It also gives you a CSS declaration you can copy into a stylesheet.
How to use
- Enter the original width and height, using the same unit for both.
- Choose a ratio preset if you already know the shape you need.
- Optionally select a new width or height and enter its pixel value.
- Read the dimensions and rounding notice, then copy the result.
What it handles
- Exact reduction: 1920 × 1080 becomes 16:9; 1366 × 768 stays 683:384.
- Five ratio presets and a swap button for portrait and landscape layouts.
- Whole-number inputs and output dimensions from 1 to 1,000,000.
- Fractional output is rounded to the nearest pixel, with a separate notice.
- Copy the ratio, CSS declaration and calculated dimensions together.
FAQ
How do I calculate a 16:9 image size?
Select 16:9, choose a new width and enter 1280. The calculated height is 720 pixels. You can also calculate the width from a known height. The ratio describes the shape, so many different pixel dimensions can share the same proportions.
Why does the result sometimes need rounding?
Pixels are whole units, but proportional arithmetic can produce a fraction. A width of 100 with a 16:9 ratio gives 56.25 for the height, rounded here to 56 pixels. That small adjustment changes the exact ratio; the notice makes this visible rather than promising perfect preservation.
Does this calculator resize my actual image?
No. It calculates dimensions without opening, changing or exporting an image. Apply the numbers in an image editor or a resizing tool. Increasing the pixel dimensions does not create missing detail, and this calculation does not estimate the resulting file size.
Can I use decimals or a different measurement unit?
This version accepts whole numbers only, from 1 to 1,000,000. Use the same unit on both sides when reducing a ratio. The optional new dimension is interpreted as pixels. Decimal separators, scientific notation and grouped numbers are rejected instead of silently reinterpreted.
Updated