Aspect Ratio Calculator
Calculate exact dimensions for any aspect ratio — perfect for videos, images, and screens.
Width
Height
Aspect ratio is the relationship between an image's width and height, and getting it wrong is why videos end up with black bars, why images stretch into distortion, and why a design looks fine on one screen and broken on another. The ratio is what stays constant when you resize correctly: a 16:9 video is 16:9 whether it is 1280×720 or 3840×2160. This calculator solves the everyday problem of keeping that relationship intact — give it a ratio and one dimension, and it computes the other, so you scale things up or down without ever distorting them or guessing at pixel counts.
How the calculator works
Enter an aspect ratio — either as a preset like 16:9 or as two numbers — and one known dimension, width or height, and the calculator returns the matching other dimension. It works in both directions and with any ratio, so you can find the height for a given width at 4:5, or the width for a 1080-pixel-tall image at 21:9. The arithmetic is simple proportion, but doing it by hand is exactly where the off-by-a-few-pixels errors that cause distortion creep in.
The proportion
For ratio W:H, given one dimension:
Height = Width × (H ÷ W)
Width = Height × (W ÷ H)
Example: 16:9 ratio, width 1920
Height = 1920 × (9 ÷ 16) = 1080
Common ratios:
16:9 widescreen 1:1 square 9:16 vertical
4:5 portrait 21:9 ultrawide 4:3 classicThe whole discipline is that both dimensions must scale by the same factor. Distortion happens the moment width and height are scaled by different amounts — stretching a 16:9 image to fill a 4:3 frame squashes everyone's faces, which is the visible symptom of a broken ratio. Black bars are the opposite: letterboxing (bars top and bottom) or pillarboxing (bars on the sides) appear when content of one ratio is placed in a frame of another without distortion, preserving the shape at the cost of empty space.
What to know about aspect ratios
- 1Match the ratio to the platform, because each one is built for a specific shape. 16:9 for YouTube and standard video, 9:16 vertical for Shorts, Reels, and TikTok, 1:1 square and 4:5 portrait for Instagram feed, 21:9 for cinematic widescreen. Uploading the wrong ratio gets your content cropped or bordered by the platform, often cutting off the part that mattered.
- 2Shoot wider than your final ratio when you can. Filming in 16:9 but knowing you also need a 9:16 vertical cut gives you room to reframe without losing resolution. Committing to one tight ratio in-camera leaves no margin, so capturing extra and cropping later is the flexible workflow for multi-platform content.
- 3Black bars are correct behavior, not an error. When a 21:9 film plays on a 16:9 screen, the bars preserve the director's framing rather than distorting it. Stretching to fill the screen would eliminate the bars but ruin every shape on screen. The bars are the honest choice; distortion is the mistake people make trying to avoid them.
- 4Keep important content inside a safe area away from the edges. Different platforms crop differently, so a subject or caption near the frame edge may be cut off when your 16:9 video is shown in a 1:1 or 9:16 context. Composing the essential elements toward the center survives cropping across ratios.
- 5The ratio stays the same at every resolution, which is the whole point. 1280×720, 1920×1080, and 3840×2160 are all 16:9, so scaling between them never distorts. When someone gives you a target width, this proportion is all you need to find the height that keeps the shape intact — no guessing, no stretching.
Frequently asked questions
What is the most common aspect ratio?
16:9 is the dominant standard for video and most screens — televisions, monitors, laptops, and YouTube all default to it. But vertical 9:16 has become equally important with the rise of Shorts, Reels, and TikTok, and Instagram favors 1:1 square and 4:5 portrait for its feed. There is no single 'most common' ratio anymore; the right one depends entirely on where the content will be shown, which is why matching platform to ratio matters.
How do I resize an image without distorting it?
Scale both dimensions by the same factor, which is exactly what preserving the aspect ratio means. If you change the width, compute the new height from the ratio rather than picking it freely — this calculator does that for you. Distortion happens only when width and height are scaled by different amounts, stretching or squashing the content. Lock the ratio, change one dimension, and let the other follow proportionally.
Why does my video have black bars?
Because its aspect ratio differs from the screen or frame it is playing in, and the player is preserving the video's true shape instead of distorting it. A 21:9 film on a 16:9 screen gets bars top and bottom (letterboxing); a 4:3 video on a 16:9 screen gets bars on the sides (pillarboxing). The bars are the correct, non-distorting way to fit one ratio inside another — the alternative would stretch the image.
What aspect ratio should I use for social media?
It depends on the platform and placement. Use 9:16 vertical for Shorts, Reels, TikTok, and Stories; 1:1 square or 4:5 portrait for Instagram feed posts; 16:9 for YouTube and horizontal video; and 4:5 often performs best for feed images because it occupies more vertical space on phones. When in doubt, shoot wider and crop to each platform's ratio, keeping the important content centered so it survives every crop.
How do I convert between two aspect ratios?
You cannot change a ratio without either cropping or adding bars — the shape is fixed by the content's dimensions. To fit a 16:9 image into a 1:1 frame, you either crop the sides off (losing content) or add bars top and bottom (keeping everything but with empty space). This calculator helps you find the exact pixel dimensions for a target ratio, and then you choose whether to crop or bar the difference.