Why this calculation matters
Every output medium has a preferred shape — a TV is 16:9, a TikTok is 9:16, an Instagram carousel is 1:1 or 4:5, a theatrical movie is 2.39:1. When you prep content for any of those targets, the question is rarely "what resolution?" — that's locked by the platform. The question is "given the aspect ratio I'm targeting and the resolution I want, what does the other dimension need to be?" That's what this calculator does.
The math is simple — width × ratio_h / ratio_w = height, or the inverse — but doing it in your head 12 times a day during a video edit is a tax on attention you don't need to pay. Bookmark this page; it's 10 seconds saved per use.
Common aspect ratios and where they're used
- 16:9 — HD TV, YouTube, monitors, modern web video. The de-facto horizontal video shape since 2009.
- 9:16 — All vertical short-form video: TikTok, Reels, YouTube Shorts, Snapchat, vertical TV walls. Birds-eye dominant format since 2020.
- 1:1 — Square posts on Instagram, Facebook, X/Twitter cards, profile photos, app icons, podcast cover art.
- 4:5 — Instagram portrait feed; the tallest aspect that doesn't get cropped in the feed. Maximizes vertical space on mobile screens.
- 4:3 — Legacy SD broadcast, old computer monitors, iPad video in some apps, vintage-look productions.
- 3:2 — DSLR and mirrorless sensor default. Standard photo prints (4×6, 6×9 inches).
- 21:9 — Ultrawide gaming monitors, cinematic web banners, extra-wide marketing hero images.
- 2.39:1 — Modern anamorphic theatrical widescreen. Most Hollywood blockbusters shoot or finish in this aspect.
- 1.85:1 — "Theatrical flat" — the standard non-anamorphic theatrical aspect. Slightly less wide than 16:9.
Watch out for the "wrong" 4K
"4K" is one term that hides two different aspect ratios. Consumer 4K (UHD, 3840×2160) is exactly 16:9 — 2× the pixel count of 1080p in each dimension. Cinema 4K (DCI 4K, 4096×2160) is closer to 1.9:1, slightly wider than 16:9. Movie cameras and DCPs use the latter; TVs and consumer cameras use the former.
If you're prepping for streaming distribution (Netflix, Amazon, YouTube), use UHD 3840×2160. If you're prepping for theatrical projection or DCP, use DCI 4K. Mixing them in the same project causes alignment headaches.
Letter-boxing and pillar-boxing — when shapes don't match
When a content's aspect ratio doesn't match its container, you either crop (lose content), stretch (distort), or pad with bars. Black bars on the top and bottom (a 4:3 video on a 16:9 monitor) is letter-boxing; black bars on the left and right (a 16:9 video on a 4:3 TV) is pillar-boxing. Both preserve the original framing without distortion.
When you can't avoid letter/pillar-boxing, you can intentionally design for it: blurred background fills (a blown-up, blurred copy of the original behind the letter-boxed video) are common on TikTok when 16:9 source is forced into a 9:16 frame.