PixelTools

Aspect Ratio Calculator

Reduces any resolution down to its simplest width:height ratio, like 16:9 or 4:3.

Width (px)

Height (px)

Aspect ratio

16:9

Common ratios: 16:9 (widescreen), 4:3 (older monitors/TVs), 21:9 (ultrawide).

What you entered

Width (px): 1920Height (px): 1080

1
Divide both dimensions by their GCD
1920:1080 ÷ GCD= 16:9

Result

Aspect ratio: 16:9

1920×1080 simplifies to an aspect ratio of 16:9.

Aspect ratios for common resolutions

The ratio is width to height reduced by their greatest common divisor. Marketing names round these off, which is why the exact ratio often looks unfamiliar.

Resolution	Exact ratio	Commonly called
1920 x 1080	16:9	16:9 widescreen
1280 x 1024	5:4	5:4
1080 x 1920	9:16	Vertical / portrait
2560 x 1080	64:27	21:9 ultrawide
3440 x 1440	43:18	21:9 ultrawide
4096 x 2160	256:135	DCI 4K / 17:9

Both ultrawide rows are sold as 21:9 but reduce to different exact ratios, so content mastered for one is slightly cropped or pillarboxed on the other.

Why aspect ratio matters for cropping

Knowing a resolution's exact aspect ratio helps you crop or resize an image or video without introducing black bars or unwanted stretching — matching the target display or format's expected ratio.

Common ratios and where they show up

16:9 is standard widescreen video and most modern monitors; 4:3 was standard for older TVs and monitors; 21:9 (or wider) shows up in ultrawide monitors and cinematic video formats.

Frequently asked questions

My image is 1920x1080 — what aspect ratio is that?

1920:1080 simplifies to 16:9, the standard widescreen ratio used by most modern monitors, TVs, and video platforms like YouTube.

I'm cropping a photo for Instagram — what ratio do I need?

Instagram supports 1:1 (square, 1080x1080), 4:5 (portrait, 1080x1350), and 16:9 (landscape, 1080x608). Stories and Reels use 9:16 (vertical, 1080x1920). Enter your crop dimensions to verify the ratio.

Why does my video have black bars on the sides?

Black bars (letterboxing or pillarboxing) appear when the video's aspect ratio doesn't match your screen's ratio. A 4:3 video on a 16:9 screen gets pillarboxed; a 21:9 ultrawide video on a 16:9 screen gets letterboxed.

How is this different from the PPI/DPI calculator?

This calculator gives you the width-to-height ratio of any resolution. The PPI calculator tells you how sharp that resolution looks on a specific physical screen size — ratio is about shape, PPI is about density.