Aspect Ratio Calculator

The GCD trick — how any dimensions become a clean ratio

An aspect ratio is fundamentally just the width and height of an image or video divided by their greatest common divisor (GCD) — the largest number that evenly divides both values without any remainder. Take 1920×1080: both numbers divide evenly by 120, giving you the familiar 16:9 ratio. Take 1080×1350: both divide evenly by 270, giving you 4:5. When the calculated GCD turns out to be unusually small relative to the actual dimensions, that's often a telling sign the source dimensions came from an irregular or non-standard crop rather than a deliberately chosen standard ratio — producing an awkward result like 137:100 instead of a clean recognizable ratio. The calculator also displays the equivalent decimal value (1.778 for 16:9, for instance), which is frequently the specific number that professional video editing software actually requests in its own settings dialogs.

The platform ratio cheat sheet — current as of 2026

16:9 (typically 1920×1080 pixels): the standard for YouTube, television broadcasts, and most business presentations. 9:16 (typically 1080×1920 pixels): the vertical standard for Instagram Reels, TikTok, YouTube Shorts, and Instagram/Facebook Stories. 1:1 (typically 1080×1080 pixels): the classic square format for feed posts across most platforms. 4:5 (typically 1080×1350 pixels): Instagram's specific portrait feed format — notably the tallest ratio the platform's feed allows, which means it claims more vertical screen real estate than a square post and tends to perform better for exactly that reason. 21:9: the cinematic ultra-widescreen format used in film and premium video content. 4:3: an older, legacy video standard still found on some tablets and older display equipment. Exporting your content in whichever ratio the destination platform natively expects ensures your content fills the entire available frame edge to edge, with no wasted space or unwanted cropping.

Letterboxing, pillarboxing, and cropping — what happens when ratios genuinely clash

Attempt to place a 16:9 landscape video into a 9:16 vertical video player, and you'll get either large, obvious black bars filling the unused space above and below (a phenomenon called letterboxing), or the platform will aggressively centre-crop the footage, potentially cutting off people's heads or important visual elements entirely (a much harsher and often more damaging outcome). The correct fix is never simply stretching the footage to fit — stretched, distorted human faces are instantly and jarringly visible to any viewer — the actual correct fix is recomposing your original shot or design specifically with the intended destination ratio already in mind from the start, then using the resize calculation section of this tool to work out the exact pixel dimensions you need to target.

If you're compressing your final exported video thumbnail or accompanying image afterward to meet a specific upload size limit, our Image Compressor handles that separate KB-based compression step cleanly.

Platform aspect ratio cheat sheet 2026

Planning multi-platform content from a single source shoot

Many content creators today need to produce the same core piece of content across several platforms with genuinely different native ratios — a single shoot destined for YouTube (16:9), Instagram Reels (9:16), and a square feed post (1:1) all at once. The most efficient professional approach is filming with the tightest, most restrictive ratio in mind first — typically 9:16 — while consciously leaving extra visual breathing room around the main subject in-frame, which then allows the same footage to be cropped outward to the wider 16:9 or 1:1 ratios afterward without losing any essential visual content, rather than the reverse approach of filming wide first and discovering critical elements fall outside the frame when cropping down to a narrower vertical ratio later.

Checking ratio before you start shooting, not after

The most common mistake creators make is discovering a ratio mismatch only after filming and importing footage into an editor — by which point reshooting is often impractical. Running your intended dimensions through this calculator before you even pick up a camera, and confirming the ratio matches your destination platform in advance, avoids the frustrating discovery of a mismatch after the footage already exists and options for fixing it have narrowed considerably.

Keeping a note of your most-used ratios

If you regularly export for the same two or three platforms, keep a quick personal note of their exact pixel dimensions rather than recalculating every time — most creators end up using the same 2-3 ratios repeatedly across nearly all of their content.

Also useful if you searched for: aspect ratio calculator, 16:9 resolution calculator, what aspect ratio is 1080x1350, 9:16 dimensions in pixels, image ratio calculator, 4:5 instagram size, video aspect ratio converter, resize keeping aspect ratio, 1920x1080 aspect ratio, aspect ratio for reels.

Frequently asked questions

Related tools