Aspect Ratio Calculator
Calculate and convert image and video aspect ratios
How to use Aspect Ratio Calculator
Calculate and convert image and video aspect ratios. Find width or height from known dimensions. Free online aspect ratio tool.
What is aspect ratio used for?
Aspect ratio is the proportional relationship between width and height. It determines how an image, video, or screen looks — too wide or too tall, and content gets cropped or letterboxed. Getting it right is essential for design, video production, and web development.
- Video production: 16:9 is the standard for YouTube, TV, and presentations. 9:16 is the vertical format for Instagram Reels, TikTok and YouTube Shorts. 1:1 is square — used for Instagram posts and profile pictures.
- Photography: Calculate crop dimensions without distorting the image. If you need a 1200×630 OG image from a 4000×3000 photo, find the optimal crop.
- Web design: Maintain consistent image proportions across responsive layouts. Calculate the CSS padding-top trick for responsive video embeds:
padding-top: 56.25%for 16:9 ratio. - Print design: Scale artwork to fit different print sizes (A4, A3, US Letter) while preserving the original proportions.
- Screen comparison: Compare monitors, phones, and tablets — a 27" 16:9 monitor vs a 27" 4:3 monitor has very different usable screen area.
Common ratios: 16:9 (widescreen video), 4:3 (classic TV/monitor), 1:1 (square), 3:2 (35mm photo), 2.39:1 (cinema widescreen), 9:16 (vertical mobile).
Frequently Asked Questions
How do I calculate aspect ratio from pixel dimensions?
Divide width by height, then simplify the fraction using the Greatest Common Divisor (GCD). For 1920×1080: GCD(1920,1080)=120, so 1920/120=16 and 1080/120=9 — giving 16:9. For 2560×1440: GCD=80, so 32:18, simplified to 16:9.
What is the CSS padding-top trick for responsive videos?
Set the container to position:relative with padding-top equal to the aspect ratio percentage (height/width × 100). For 16:9: padding-top:56.25%. The video inside is position:absolute filling the container. This maintains the ratio at any width without JavaScript.
What resolution should I use for a 16:9 video?
Standard: 1280×720 (720p). Full HD: 1920×1080 (1080p). 4K: 3840×2160. For social media thumbnails: 1280×720 minimum. For YouTube: 1920×1080 recommended. Always upload at the highest quality your workflow supports.
Why do old movies have black bars on modern screens?
Movies filmed at 4:3 (1.33:1) or even older ratios (1.37:1 Academy ratio) do not fill 16:9 screens. Black bars (pillarboxing) appear on the sides. Conversely, 21:9 ultra-wide cinema content gets horizontal black bars (letterboxing) on 16:9 screens.
What aspect ratio should I use for social media images?
Facebook feed: 1.91:1 or 1:1. Instagram feed: 1:1 (square) or 4:5 (portrait). Instagram Stories/Reels: 9:16. Twitter/X: 16:9. LinkedIn: 1.91:1. Pinterest: 2:3 (portrait performs best). Always check each platform's current specifications as they update frequently.
Aspect ratio calculator vs image resizer vs crop tool
An aspect ratio calculator computes dimensions mathematically — it tells you what size to use. An image resizer actually changes the pixel dimensions of an image file. A crop tool (Photoshop, GIMP, Canva) removes parts of the image to achieve a target ratio. Use the calculator first to plan your dimensions, then apply them with an image editing tool.