What does an aspect ratio like 16:9 mean?

An aspect ratio is the proportion of width to height, written as two whole numbers. 16:9 means that for every 16 units of width there are 9 units of height. It does not fix the pixel size, only the shape, so 1280 by 720 and 1920 by 1080 are both 16:9.

How do I calculate the missing dimension for a given ratio?

Multiply the known dimension by the ratio of the other side. For 16:9, height equals width times 9 divided by 16, and width equals height times 16 divided by 9. The tool does this for you and rounds to whole pixels.

What aspect ratio should I use for social media video?

Vertical platforms like TikTok, Instagram Reels, and YouTube Shorts use 9:16, typically 1080 by 1920 pixels. Square 1:1 works for feed posts, and 16:9 suits landscape YouTube and most embedded players.

Why do I get black bars on my video?

Black bars, called letterboxing or pillarboxing, appear when the video's aspect ratio differs from the display's. A 4:3 clip on a 16:9 screen gets bars on the sides. Match the export ratio to the target surface to avoid them, or crop to fit.

What is the 2.39:1 ratio used for?

2.39:1 is the modern anamorphic widescreen cinema standard, giving the very wide cinematic look. It is wider than 21:9 ultrawide monitors and is common in feature films and cinematic game cutscenes.

Aspect Ratio Reference

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Whether you are exporting a video, sizing a thumbnail, or buying a monitor, the aspect ratio decides the shape of the frame. This reference lists every common ratio with its typical use and example resolutions, and includes a helper to compute the exact pixel dimensions for any ratio.

How it works

An aspect ratio is simply width divided by height, reduced to the smallest whole numbers. A 1920 × 1080 frame has a ratio of 1920 / 1080 = 16/9, so it is written 16:9. The ratio fixes the shape, not the size — every 16:9 resolution from 1280 × 720 up to 3840 × 2160 has the same proportions.

To find a missing dimension while keeping the ratio, scale by the opposite side:

height = width  × (ratioH / ratioW)
width  = height × (ratioW / ratioH)

For a 16:9 frame 2560 px wide, the height is 2560 × 9 / 16 = 1440 px. The tool applies this for whichever dimension you supply and rounds to whole pixels.

Example and notes

If your source footage is 4:3 but your target is 16:9, you will either see pillarboxing (black bars at the sides) or you must crop the top and bottom. Matching the export ratio to the destination surface avoids both. For multi-platform delivery, master in the widest ratio you need and crop down — 16:9 masters crop cleanly to 1:1 and 9:16.

Common gotcha: 16:10 and 16:9 look almost identical but are not — a 16:9 image stretched onto a 16:10 panel will appear slightly squashed vertically. Always confirm both source and target ratios before scaling.