Vertical Aspect Ratio Guide

Choosing the right aspect ratio is one of the first decisions in AI video generation, and it significantly impacts how your content performs on each platform. Vertical video dominates short-form content, but the exact dimensions matter: 9:16, 4:5, and 1:1 each have specific use cases and advantages.

This guide explains which aspect ratio to use for each platform, how aspect ratio affects AI generation quality, and how to efficiently repurpose content across multiple platforms.

Aspect Ratios by Platform

TikTok: 9:16 (Full Vertical)

TikTok is designed for 9:16 (1080x1920). This ratio fills the entire screen on mobile devices, maximizing immersion. Using any other ratio results in letterboxing (black bars) that reduce visual impact.

Instagram Reels: 9:16 (Primary), 4:5 (Acceptable)

Reels also favor 9:16 for full-screen playback. However, Instagram supports 4:5 (1080x1350) for feed posts, which can be useful for cross-platform strategies. Note that 4:5 content in Reels will have pillarboxing.

YouTube Shorts: 9:16 (Required)

YouTube Shorts requires 9:16. Other vertical ratios may not qualify as Shorts and will be treated as regular vertical videos, losing the Shorts algorithm advantages.

Instagram Feed: 4:5 (Vertical), 1:1 (Square)

For feed posts (not Reels), 4:5 is the tallest vertical ratio Instagram displays without cropping. Square 1:1 (1080x1080) remains popular for its flexibility but takes up less screen space.

Facebook & LinkedIn: 4:5 (Safe Bet)

These platforms are more flexible but 4:5 works reliably across both for vertical content without unexpected cropping.

Quick Reference Table

How Aspect Ratio Affects AI Generation Quality

Your choice of aspect ratio impacts more than just platform fit—it affects how the AI model generates content:

Subject framing

• 9:16: Vertical framing naturally centers subjects with less horizontal space. Good for portraits, full-body shots, and products.
• 4:5: Slightly wider, giving more context for horizontal elements while still being vertical.
• 1:1: Equal space in all directions. Good for flat lays, overhead shots, and balanced compositions.

Motion and camera movement

• Vertical formats exaggerate vertical motion: Push-ins and tilts feel more dramatic in 9:16.
• Pan movements are constrained: There is less horizontal space for pans to reveal information.
• Center-framing is safest: With limited width, centering your subject prevents awkward cropping.

Cross-Platform Repurposing Strategy

Creating separate versions for every platform is time-consuming. Use these strategies to work smarter:

Generate in 9:16 first (master format)

9:16 is the most restrictive format. Generating in this ratio first ensures your content works on TikTok, Reels, and Shorts without modification. You can later crop or pad for other platforms.

Crop 9:16 to 4:5 for Instagram feed

Extract the central portion of your 9:16 video. This maintains focus on your subject while fitting Instagram feed dimensions.

Pad 4:5 to 9:16 when necessary

If you have 4:5 content that needs to work on TikTok, add blurred edges or a gradient background to fill the vertical space. This is less ideal but functional.

Square for universal compatibility

1:1 displays acceptably on all platforms (with letterboxing). Use this when you need maximum compatibility but accept suboptimal presentation.

Aspect Ratio Prompting Tips

When generating AI video, specify your intended aspect ratio in your prompt to help the model compose appropriately:

For 9:16 vertical

Vertical 9:16 composition. A [subject] centered in frame, full body visible, minimal negative space on sides, clean top and bottom margins for UI overlays.

For 4:5 feed

Square-ish vertical 4:5 composition. A [subject] with some horizontal context, balanced framing, room for captions below subject.

For 1:1 square

Square 1:1 composition. A [subject] arranged with equal visual weight on all sides, flat lay or centered portrait, balanced negative space.

Common Aspect Ratio Mistakes

• Generating in 16:9 then cropping: You lose important visual information. Always generate in your target ratio when possible.
• Assuming all vertical is the same: 9:16, 4:5, and 1:1 behave differently on each platform. Know your primary platform.
• Ignoring safe areas: TikTok and Instagram have UI overlays (like buttons, captions, hashtags). Keep important content away from edges.
• Switching ratios mid-project: Consistency matters for brand and series content. Pick one ratio and stick with it.

Related Resources

• Generator: vertical video generator
• Guide: vertical 9:16 stability guide
• Platform: YouTube Shorts guide
• Templates: TikTok hook templates
• Output: resolution & quality

FAQ

Which aspect ratio should I use for viral content?

9:16 is the safest bet for viral potential because it works natively on TikTok, Reels, and Shorts—the three main short-form video platforms.

Can I change aspect ratio after generation?

You can crop or pad, but changing aspect ratio fundamentally changes the composition. Always generate in your target ratio for best results.

Why does my content look different on Instagram vs TikTok?

Each platform processes video slightly differently and has different UI overlays. Test your content on each platform to understand how your chosen ratio appears.

Should I generate multiple ratios for the same content?

Only if you have a clear multi-platform strategy. For most creators, generating once in 9:16 and adapting for other platforms is more efficient.

What is the safest aspect ratio for beginners?

9:16 vertical. It works everywhere short-form content matters and is the expected format for TikTok, Reels, and Shorts.