Aspect ratio calculator — simplify a size and resize without stretching

How to use the aspect ratio calculator

1. Enter the Width and Height of the original image, video or screen.
2. Under Resize, keep Just the ratio, or choose New width → height or New height → width.
3. If resizing, enter the New width or New height.
4. Read the Aspect ratio, As a decimal and, if you resized, Resized. The table lists widths for heights of 480, 720, 1080, 1440 and 2160.

What it does and when to use it

The aspect ratio is the shape of a picture: how wide it is compared with how tall. Keeping it the same when you resize stops faces and logos from looking stretched or squashed. The calculator helps when you need to:

• scale a photo for a website to a set width without distortion,
• check whether a video is 16:9, 4:3 or something else before uploading,
• find the right size for a thumbnail, banner or slide,
• compare screens with different resolutions.

Once you know the target size, the image resizer can do the actual resize in your browser. To see how sharp a screen of a given size will look, the PPI calculator gives pixel density. And if you are printing at a set size, the DPI checker shows the print resolution of an image file.

How it works

Simplifying. The calculator divides width and height by their greatest common divisor. For 1920 × 1080 the divisor is 120, giving 16:9. To handle decimals it first multiplies both numbers by 100 and rounds.

Decimal form. Width ÷ height, shown to four decimal places with “: 1” after it.

Resizing.

• New height = new width × original height ÷ original width
• New width = new height × original width ÷ original height

Results are shown to two decimal places, so you can see when a size does not land on a whole pixel.

Worked examples

These figures come from the calculator’s own function.

Full HD. 1920 × 1080 gives an aspect ratio of 16:9, or 1.7778 : 1. The table shows 1280 × 720, 2560 × 1440 and 3840 × 2160 as the same shape.

Scaling a 16:9 video down. 1920 × 1080 with a new width of 1280 gives Resized: 1280 × 720.

An older 4:3 screen. 1024 × 768 reduces to 4:3. With a new height of 600, the width becomes 800, giving 800 × 600.

An ultrawide monitor. 3440 × 1440 reduces to 43:18, or 2.3889 : 1.

Limits and tips

• Pixels are whole. When a result has decimals, round it, and accept a tiny change of shape, or crop slightly instead.
• Pixel aspect is assumed square. Some older video formats use non-square pixels; this tool does not adjust for them.
• Crop versus resize. Changing the ratio itself (for example 16:9 to 1:1 for a square post) needs cropping, not resizing.
• Everything runs in your browser.