Aspect Ratio Calculator
Resize dimensions while keeping the aspect ratio locked, and see the simplified ratio.
How to use
- Enter the original width and height.
- Type a new width or new height.
- The other dimension fills in to keep the ratio; the simplified ratio is shown.
How the Aspect Ratio Calculator works
Works out missing width or height while preserving an aspect ratio, and reduces a pixel dimension to its simplest ratio form.
Scaling is a proportion: new height is new width times original height over original width. The simplified ratio comes from dividing both dimensions by their greatest common divisor.
new height = new width × (original height ÷ original width)
Worked example
Resizing 1920×1080 to 1280 wide gives 1280 × 1080/1920 = 720. The greatest common divisor of 1920 and 1080 is 120, so the ratio simplifies to 16:9.
Things worth knowing
- Common ratios: 16:9 video and most screens, 4:3 older displays, 1:1 social square, 9:16 vertical mobile, 21:9 ultrawide, 1.85:1 and 2.39:1 cinema.
- Rounding to whole pixels can shift the ratio very slightly — unavoidable, since pixels are discrete.
- Changing aspect ratio rather than scale means cropping or letterboxing; there is no way to avoid one or the other.
Frequently asked questions
How do I keep the same aspect ratio?
Change one new dimension and the calculator computes the other so the proportions stay identical.
What does 16:9 mean?
It's the simplified ratio of width to height — common for widescreen video.
How do I find the ratio of an arbitrary size?
Divide both numbers by their greatest common divisor. 1600×1200 divided by 400 gives 4:3.