Help
FAQ
Short answers about ratios, pixels, and how this calculator treats your numbers.
How do I use this aspect ratio calculator?
Pick a ratio (16:9, 9:16, 1:1, or type 1920×1080). Enter a width or a height — not both from scratch. RatioFit computes the missing side in whole pixels. The last field you type is the lock.
How do I calculate height from width and a ratio?
Height = width × (ratio height ÷ ratio width). For 16:9, height = width × 9 ÷ 16. A 1920-pixel width becomes 1080. For 9:16, height = width × 16 ÷ 9, so 1080 wide becomes 1920 tall.
How do I calculate width from height?
Width = height × (ratio width ÷ ratio height). A 1080-tall 16:9 frame is 1920 wide. A 1920-tall 9:16 frame is 1080 wide.
Can I paste 1920×1080 instead of 16:9?
Yes. The ratio field accepts 16:9, 16/9, 1.777, or a pixel pair like 1920×1080 or 1920x1080. Pixel pairs also fill both dimension fields.
What pixel size is 16:9?
Common 16:9 sizes are 1280×720 (720p), 1920×1080 (1080p), 2560×1440 (1440p), and 3840×2160 (4K). Any pair that simplifies to 16:9 is valid.
What size should I export for TikTok, Reels, and Shorts?
Use 9:16 at 1080×1920 unless a brief says otherwise. That fills the phone screen on TikTok, Instagram Reels, and YouTube Shorts.
4:5 or 9:16 for Instagram?
4:5 (1080×1350) is the tallest feed post. 9:16 (1080×1920) is Stories and Reels. Posting 9:16 into the feed usually gets cropped toward 4:5.
Will this stretch my video?
No. The calculator only returns dimensions that keep the ratio. If your source is a different ratio, you must crop or letterbox — changing one side independently is what causes stretch.
Does RatioFit upload my files or need an account?
No. It is a static page. Math runs in your browser. Nothing you type is sent to a server. There is no login.
Is the aspect ratio calculator free?
Yes. RatioFit is free to use. The site is AdSense-ready and may show ads when a publisher ID is configured. The tool itself is not paywalled.
Still stuck? Write to us or open the calculator with a sample like 1920×1080.