Aspect Ratio Calculator
How it works
Enter any width and height and the tool reduces them to the lowest equivalent ratio (1920 × 1080 becomes 16:9). Click the lock icon to keep the ratio fixed: change either dimension and the other follows, so you don't end up with a stretched image. Click any preset (YouTube thumbnail, Instagram post, TikTok video, LinkedIn banner, A4 portrait, …) and the dimensions are filled in for you.
The simplification uses the standard greatest-common-divisor algorithm: gcd(1920, 1080) = 120, so 1920/120 : 1080/120 = 16:9. Non-integer inputs (3840.5 × 2160) and very small or very large numbers are handled correctly. Negative inputs are rejected.
Why aspect ratio matters: every platform has a target ratio for hero images, thumbnails, video and posts. Upload a photo at the wrong ratio and the platform either letterboxes it (black bars), crops your subject out, or stretches the pixels, and on every social network that happens silently with no preview. Knowing the target ratio before you crop is the difference between an image that looks intentional and one that looks broken.
A few practical tips: • For social media stick to the platform's recommended dimensions exactly. Instagram's "4:5" portrait post is 1080 × 1350, and anything else gets cropped. • For video the universal default is 16:9 (1920 × 1080 HD, 3840 × 2160 4K). Vertical short-form (TikTok, Reels, Shorts) is 9:16 (1080 × 1920). • For ads Google Ads and Facebook Ads set several ratio targets per campaign, so run the same hero image through the 16:9, 4:5 and 1:1 presets to have all three sizes ready. • For print the most common photo paper is 4:6 (10×15 cm) or 5:7 (13×18 cm); A4 is roughly √2:1 (297:210 ≈ 1.414:1), not 16:9, so sending a 16:9 image to A4 print leaves big white margins.
Frequently Asked Questions
How is the ratio simplified?
- The tool divides width and height by their greatest common divisor (GCD). 1920 × 1080 gives gcd(1920,1080) = 120 and therefore 16:9. 1080 × 1080 gives 1:1. 4080 × 2720 gives gcd(4080,2720) = 680, then 6:4, reduced to 3:2.
What social media presets are included?
- YouTube thumbnail (1280 × 720, 16:9), Instagram square post (1080 × 1080, 1:1), Instagram portrait post (1080 × 1350, 4:5), Instagram story / Reel (1080 × 1920, 9:16), TikTok video (1080 × 1920, 9:16), Twitter / X header (1500 × 500, 3:1), Twitter post image (1200 × 675, 16:9), Facebook cover (820 × 312), Facebook post (1200 × 630), LinkedIn banner (1584 × 396, 4:1), LinkedIn post (1200 × 627), Pinterest pin (1000 × 1500, 2:3).
What's the difference between 16:9 and 16:10?
- Tiny but visible. 16:9 (1.78:1) is the universal video standard since HDTV; 16:10 (1.6:1) is a slightly taller ratio that some laptop and tablet screens use. A 16:9 video letterboxed on a 16:10 screen gets thin black bars top and bottom, and a 16:10 image stretched to 16:9 shows visibly squashed circles.
Why is 1:1 popular on Instagram?
- Because square 1:1 was Instagram's original (and only) supported ratio from 2010 to 2015. It still works on every platform, looks identical in feed and on the profile grid, and is the safest fallback when you are unsure of the target. 4:5 (Instagram portrait) takes more screen space in feed and is now the recommended default for most posts.
How do I keep the same aspect ratio when resizing?
- Click the lock icon between the width and height fields. With the lock on, changing either dimension auto-adjusts the other to preserve the current ratio. That is what you want when you have a target width (CSS max-width: 1200px, say) and need the matching height for the original photo.
What aspect ratio for a YouTube thumbnail?
- 16:9 at 1280 × 720 minimum, which is the tool's preset. YouTube accepts up to 1920 × 1080 but compresses thumbnails server-side, so 1280 × 720 is the sweet spot. Anything other than 16:9 gets letterboxed in feed previews.
Is my data stored anywhere?
- No. The tool is a pure JavaScript calculator: every input is processed locally and discarded when you leave the tab. There is no backend, no analytics tied to the dimensions you type, and DevTools → Network confirms zero outbound requests.
Common aspect ratios: what to use where
Reference for picking the right aspect ratio before cropping or rendering. Dimensions are the platform's recommended exact pixel sizes; the ratio is what to use when you need to compute custom dimensions.
| Ratio | Decimal | Common dimensions | Best for |
|---|---|---|---|
| 16:9 | 1.778 | 1920 × 1080, 1280 × 720, 3840 × 2160 | HD video, YouTube, TVs, projectors, monitors |
| 9:16 | 0.563 | 1080 × 1920 | TikTok, Instagram Reels, YouTube Shorts (vertical video) |
| 1:1 | 1.000 | 1080 × 1080 | Instagram square post, Twitter post, profile pictures |
| 4:5 | 0.800 | 1080 × 1350 | Instagram portrait post (recommended default) |
| 3:2 | 1.500 | 1500 × 1000, 6000 × 4000 | DSLR / mirrorless cameras, photo prints (10×15) |
| 4:3 | 1.333 | 1024 × 768, 1600 × 1200 | Older displays, iPads, presentations, classic TV |
| 21:9 | 2.333 | 2560 × 1080, 3440 × 1440 | Ultrawide monitors, cinematic video |
| 2.39:1 | 2.390 | varies | Cinemascope / anamorphic film |
| 3:1 | 3.000 | 1500 × 500 | Twitter / X header banner |
| 4:1 | 4.000 | 1584 × 396 | LinkedIn personal banner |
| √2:1 | 1.414 | 210 × 297 mm (A4) | ISO paper sizes (A0–A10), European print |
| 8.5:11 | 0.773 | 2550 × 3300 (300dpi) | US Letter print |
| 5:7 | 0.714 | 1500 × 2100 | Photo print 13×18 cm, portrait wedding photos |
| 6:7 | 0.857 | varies | Some medium-format cameras |
| 1.91:1 | 1.910 | 1200 × 630 | Open Graph / Facebook link preview, Twitter card |
| 2:3 | 0.667 | 1000 × 1500 | Pinterest pins, book covers |
| 3:4 | 0.750 | 1080 × 1440 | Smartphone portrait photos (default ratio on most phones) |
Platform recommendations as of 2026. Social networks update target sizes occasionally. Always cross-check the current platform docs before launching a paid ad campaign.