Aspect Ratio Calculator
Calculate aspect ratios instantly. Convert dimensions, solve for missing sides, and browse 2025/2026 social media image sizes.
Calculator
Solve for Missing Side
Enter a ratio and one dimension to calculate the other.
You just tested your Aspect Ratio Calculator — Try Monitor Refresh Rate next →
What Is an Aspect Ratio Calculator?
An aspect ratio describes the proportional relationship between width and height: 16:9 is the modern HDTV / monitor / video standard (1920x1080, 2560x1440, 3840x2160); 4:3 was the analog TV and pre-iPhone laptop format; 21:9 is the ultrawide cinema and gaming-monitor ratio (also called 2.35:1); 1:1 is the Instagram-square / app-icon / profile-picture norm; 9:16 is vertical-first short-form video (TikTok, Reels, YouTube Shorts); 3:2 is the classic 35mm film and modern DSLR sensor ratio; 2:3 is the Pinterest pin format. The calculator simplifies any pixel dimensions to a lowest-terms ratio using GCD (1920x1080 -> 16:9 via gcd=120), solves for the missing side when you know one dimension and a target ratio (cross-multiplication: width = height * W/H), and ships with a 2026-current reference table of platform-specific dimensions for Instagram, TikTok, YouTube, X, LinkedIn, Pinterest, and Threads — including the new IG Reel cover that ships as 1080x1920 9:16 not the legacy 1:1 grid thumbnail.
How to Use the Aspect Ratio Calculator
Open the Calculator tab. Enter width and height in pixels — the simplified ratio appears live with the GCD shown. To solve a missing side: enter a target ratio (e.g., 16:9 or 1.78) and one dimension; the other computes via cross-multiplication. The visual preview renders a scaled rectangle in the chosen ratio so you can sanity-check before exporting. Switch tabs to Social Media Sizes for a one-tap copy of current platform dimensions (auto-updated against each platform's spec page). The CSS Snippet tab generates the aspect-ratio CSS property declaration plus object-fit and object-position fallbacks for older browsers — paste straight into your stylesheet. The Image fit comparator on the right shows cover (fill the box, crop overflow), contain (letterbox to fit), fill (stretch to fit, distorts), scale-down (smaller of contain/none), and none (no resize) side-by-side on a sample image — useful for picking the right CSS value when your image and container ratios don't match.
Why Aspect Ratios Matter for Every Screen
Mismatched aspect ratios cause the two most-flagged Core Web Vitals failures: Cumulative Layout Shift (CLS) when an image loads at a different ratio than the placeholder predicted, and Largest Contentful Paint (LCP) when the hero image must be re-laid out mid-paint. The fix is the aspect-ratio CSS property (or width/height attributes on <img>) which lets the browser reserve the right box before the image bytes arrive. On the social side, Instagram crops anything not 4:5 or 1:1 in feed view; TikTok crops anything not 9:16 in the For You feed; YouTube Shorts requires 9:16 between 1080x1920 and 720x1280 — uploading a 16:9 file gets pillarboxed with black bars and slashes engagement by 30-40% versus a native-ratio upload (per Meta and TikTok 2024 creator-success reports). Print is unforgiving too: a 3:2 photo printed to a 4:6 frame loses 8% of the image to bleed if you do not pre-crop. The calculator's job is to surface the mismatch before you spend an hour fixing it after the fact.
Frequently Asked Questions
What is an aspect ratio?
An aspect ratio is the proportional relationship between width and height, expressed as W:H (e.g. 16:9). It describes shape, not size — 1920x1080 and 640x360 both have a 16:9 ratio.
How do I maintain aspect ratio when resizing?
Use the solver: enter your ratio and the known side. The calculator solves for the missing dimension using cross-multiplication, ensuring the ratio stays exact.
What aspect ratio should I use for social media?
It depends on the platform. Instagram square posts use 1:1, stories use 9:16, YouTube thumbnails use 16:9, and Twitter/X posts use 16:9. Check the Social Media Sizes tab for full 2025/2026 reference.
Use this tool inside a bigger workflow
These collections group follow-up tools and guides that commonly belong in the same job.
Browse same tags
Jump to other tools that share the same workflow, format, or use case.