What is an Aspect Ratio Calculator?
An aspect ratio calculator helps you find the proportional relationship between width and height — and lets you calculate missing dimensions when you know the ratio. It's essential for web development (responsive images, video embeds), graphic design (resizing without distortion), video production (matching resolution standards), and social media (each platform has different required ratios).
How to Use the Aspect Ratio Calculator
Mode 1 (Width × Height → Ratio): Enter any width and height to find the simplified ratio. For example, 1920×1080 → 16:9. Mode 2 (Ratio → Dimensions): Enter a ratio (like 16:9) and a known width or height, and the calculator computes the other dimension. Use the presets for common ratios like 16:9 (HD video), 4:3 (classic TV), 1:1 (square), or 9:16 (mobile video).
Formula Used
Find ratio: GCD(width, height) → ratio_w = width/GCD, ratio_h = height/GCD
Find height from ratio: height = width × (ratio_h / ratio_w)
Find width from ratio: width = height × (ratio_w / ratio_h)
GCD (Euclidean): GCD(a,b) = GCD(b, a mod b) until remainder = 0
Common Aspect Ratios and Their Uses
- 16:9 — YouTube, TV, monitors, laptops. Common resolutions: 1280×720, 1920×1080, 3840×2160
- 4:3 — Classic TV, older monitors, some tablet formats
- 1:1 — Instagram square posts, profile pictures, icons
- 9:16 — Instagram Reels, TikTok, YouTube Shorts, Snapchat (vertical mobile)
- 4:5 — Instagram portrait posts (taller than square, gets more feed space)
- 3:2 — DSLR cameras (standard 35mm film frame), some tablets
- 21:9 — Ultra-wide monitors, cinematic widescreen films
Frequently Asked Questions
What is aspect ratio?
The proportional relationship between width and height (W:H). 16:9 means 16 units wide for every 9 units tall. The same ratio applies at any size: 1920×1080 and 3840×2160 both equal 16:9.
What is the standard YouTube video aspect ratio?
16:9. Recommended: 1920×1080 (1080p), 3840×2160 (4K). YouTube Shorts: 9:16 vertical. Other ratios get letterboxed/pillarboxed to fit the 16:9 player.
What is the difference between 4:3 and 16:9?
4:3 is squarish (classic TV). 16:9 is wide (modern screens). 16:9 provides 33% more horizontal content at the same height. Old 4:3 content on 16:9 shows vertical black bars.
How do I maintain aspect ratio when resizing images with CSS?
Use aspect-ratio CSS property: width: 100%; aspect-ratio: 16/9;. Or set only width and let height: auto handle the other dimension. Supported in all modern browsers since 2021.
What aspect ratio should I use for Instagram posts?
Square (1:1) = classic. Portrait (4:5) = more feed space, 1080×1350px — recommended. Stories/Reels: 9:16 vertical, 1080×1920px.
What is a 21:9 ultra-wide aspect ratio?
Ultra-wide monitors and cinematic film format. Common resolutions: 2560×1080, 3440×1440. Shows 31% more horizontal content than 16:9 at the same height.
How do I calculate height from width and aspect ratio?
Height = Width × (ratio_H / ratio_W). For 16:9 at 1280px wide: 1280 × (9/16) = 720px.
How do I find the aspect ratio of an image or video?
Divide width and height by their GCD. For 1920×1080: GCD = 120, so 1920÷120 = 16, 1080÷120 = 9 → 16:9. Our calculator does this automatically.