Answer: Enter your values and the Video Aspect Ratio Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Get the right dimensions for any platform
Aspect ratio is the proportional relationship between a video's width and height, expressed as width:height. 16:9 is the widescreen standard for YouTube, TVs, and nearly all online video; 9:16 is the vertical format of Shorts, Reels, and TikTok; 4:3 is the legacy television and older YouTube era; 21:9 and wider appear in cinematic and ultrawide contexts; and 1:1 square video serves feed placements on social platforms. This calculator converts between width, height, and ratio so you can resize, letterbox, or crop footage to any target.
The arithmetic is a proportion. Given width and height, the ratio is width ÷ height reduced to lowest terms (1920 ÷ 1080 = 16 ÷ 9). Given a ratio and one dimension, the other is a cross-multiplication: at 16:9, a height of 1080 implies width = 1080 × 16 ÷ 9 = 1920. The tool also computes pixel count (width × height) for quick resolution comparisons and detects the nearest common ratio for any odd dimensions you feed it.
Where the practical confusion lives: containers versus pixels. A 16:9 player can display 4:3 content by pillarboxing (bars left and right) or a 2.35:1 film by letterboxing (bars top and bottom). Anamorphic formats add another wrinkle — the pixels are stored stretched and displayed at a different ratio — which is why a file's stored dimensions can mislead about its display ratio without the metadata.
To use the calculator, enter any two of width, height, and ratio — the third is solved for you, along with total pixel count. A common workflow: type your source resolution, pick the target ratio such as 9:16 for vertical clips, and read off the largest matching dimensions that keep your pixels within bounds.
Check your export settings against the result as well: player-side scaling cannot add detail, so downscaling a 16:9 master to 9:16 in your editor — rather than letting a platform crop the center automatically — keeps control over what stays in frame and what gets cut.
The table pairs each standard ratio with its canonical resolutions. YouTube accepts a range of 16:9 resolutions from 4K down, and its player letterboxes anything non-16:9 automatically; vertical 9:16 uploads to a normal video are shown with pillarbox bars unless published as Shorts.
Resolution names come from the shorter dimension: 1080p means 1080 lines of vertical resolution. 4K UHD is 3840 × 2160 (16:9); DCI 4K is 4096 × 2160 (roughly 1.9:1), a cinema format distinct from consumer UHD — a distinction that matters when matching footage to deliverables.
Converting between ratios means cropping, padding, or distorting — the calculator shows the exact dimensions for each clean path. Going from 16:9 to 9:16 by center-cropping keeps full height but discards the left and right thirds (1920-wide source becomes effectively 607-pixel-wide usable area at 1080 height). Going from 16:9 to 1:1 keeps 1080 × 1080 from the center. Padding preserves all content at the cost of bars. Distorting — stretching to fill — is almost never correct for people and text.
The professional workflow for repurposing horizontal footage vertically is not a blind crop: reframe shot by shot so the subject stays in frame, since a center crop presumes a centered subject. This is why editors treat the calculator's numbers as the geometry constraint and make the framing decision creatively.
| Aspect ratio | Common resolutions | Where used |
|---|---|---|
| 16:9 | 1920×1080, 3840×2160 | YouTube, TV, most online video |
| 9:16 | 1080×1920 | Shorts, Reels, TikTok |
| 1:1 | 1080×1080 | Feed posts |
| 4:3 | 1440×1080, 640×480 | Legacy TV, MFT cameras |
| 21:9 | 2560×1080, 3440×1440 | Ultrawide displays, scope video |
The same math governs stills and screens. Full-frame and most mirrorless cameras shoot 3:2; Micro Four Thirds is 4:3; smartphones typically capture 4:3 with 16:9 as a cropped option. Computer displays follow the same ratios — 16:9 dominates, 16:10 (as in many laptops) gives slightly more vertical room, and 21:9 ultrawides approximate cinema scope. When a photo's ratio differs from the display's, the same letterbox/pillarbox logic applies.
What is the aspect ratio of 1920×1080?
16:9 — divide both numbers by 120 (1920 ÷ 120 = 16, 1080 ÷ 120 = 9). It is the standard widescreen HD resolution used by YouTube and most online video.
How do I convert 16:9 video to 9:16?
Either center-crop to 1080 × 1920 (discarding the left and right of the frame) or pad the full 16:9 image with bars above and below. Cropping keeps full sharpness; padding keeps full content. Reframe per shot if subjects aren't centered.
What resolution should vertical Shorts be?
1080 × 1920 (9:16) is the standard vertical resolution for YouTube Shorts, Instagram Reels, and TikTok.
How do I calculate aspect ratio from width and height?
Divide width by height and reduce: 2560 ÷ 1080 = 2.370 ≈ 21:9. Or express it as a decimal multiplier (2.37x) when the exact ratio isn't a common one.
Why do black bars appear on videos?
The video's ratio differs from the display's, so the player letterboxes (bars top/bottom for wider content) or pillarboxes (bars left/right for narrower content) rather than stretch the image.