About Aspect Ratio Calculator
Calculate and convert aspect ratios. Scale dimensions while maintaining proportions. Common presets included. Free, no sign-up required.
How to use
- Enter your starting Width and Height in the top input pair. Any pixel values work — 1920x1080, 4032x3024 from a phone camera, or arbitrary numbers. The simplified ratio is computed via the Euclidean GCD algorithm and shown beneath.
- Use the preset chips (16:9, 4:3, 1:1, 21:9, 9:16, 3:2) to lock the calculator to a known target ratio. The preset rewrites the top pair to a canonical example and locks the proportion for the scaling section.
- In the New Width / New Height pair, type one dimension and the other auto-fills to maintain the locked ratio. Useful for resizing a 1920x1080 master to fit a 1280-wide column while keeping 16:9 exact.
- Read the ratio output to identify standard formats: 16:9 is HD/4K video and most YouTube content, 4:3 is legacy TV and iPad, 21:9 is ultrawide cinema, 1:1 is Instagram square, 9:16 is Stories/Reels/TikTok, and 2.39:1 is anamorphic cinemascope.
- For typography vertical rhythm, plug in your line-height pixel total as Height and column width as Width — the GCD reveals whether your grid resolves cleanly or carries a rounding remainder that will accumulate down the page.
- Bookmark the page or copy the resulting dimensions into your CSS (aspect-ratio: 16/9), Figma frame, or ffmpeg -vf scale arguments. The math runs entirely client-side, so the page works offline once cached.
Examples
Resize 1920x1080 to fit a 1280px column
Enter 1920 and 1080 — output reads 16:9 (GCD 120). Type 1280 in New Width and New Height auto-fills 720. The 1280x720 result is the standard 720p HD frame, exactly half the 1080p area but identical aspect.
Find the GCD of an odd resolution
A 4032x3024 iPhone capture simplifies to 4:3 (GCD 1008). Many DSLR sensors are also 4:3 native. To export a 16:9 crop you would lose 567 pixels of vertical or 504 horizontal — useful for planning safe-area composition.
Vertical-video TikTok target
Hit the 9:16 preset, then type 1080 in New Width — New Height becomes 1920. That is the ideal Stories/Reels/TikTok upload size; smaller sources will be upscaled by the platform and lose sharpness.
Frequently asked questions
How does the calculator find the simplified ratio?
It runs the Euclidean algorithm on the width and height: repeatedly replace the larger number with the remainder of dividing it by the smaller, until the remainder is zero. The last non-zero divisor is the greatest common divisor, and dividing both inputs by it yields the canonical ratio. For 1920x1080 the GCD is 120, giving 16:9. The algorithm runs in microseconds even for huge resolutions.
When should I use 16:9 versus 21:9 versus 2.39:1?
16:9 (1.78:1) is the universal video standard for HDTV, YouTube, streaming, and most monitors. 21:9 (2.33:1) is ultrawide gaming and productivity displays. 2.39:1 (often called CinemaScope or anamorphic) is theatrical feature film aspect — it appears wider than 21:9 because it really is, by about 3 percent. Use 2.39:1 only when you intend to letterbox; otherwise stick with 16:9 for delivery and 17:9 (DCI 4K) for theatrical masters.
Why does my CSS aspect-ratio property render at slightly different dimensions than expected?
CSS aspect-ratio computes the longer dimension from the shorter one using floating-point math, then sub-pixel rounds for layout. A 1000px-wide container with aspect-ratio: 16/9 will render at 562.5px tall, which the browser may snap to 562px or 563px depending on device pixel ratio. To avoid surprises, set both width and height explicitly when sub-pixel accuracy matters, or use integer-friendly multiples like 1280x720 and 1920x1080.
How do social platform aspect ratios actually render?
Instagram feed accepts 1:1, 4:5 (portrait), and 1.91:1 (landscape) — anything else gets cropped. Stories and Reels are 9:16 at 1080x1920. YouTube is 16:9 at 1920x1080 minimum (4K is 3840x2160). LinkedIn posts: 1.91:1 for landscape, 1:1 for square. Twitter/X images: 16:9 ideal, 2:1 also accepted. Pinterest pins: 2:3 vertical (1000x1500). Always design for the tightest crop platform first.
Can I use this for non-image things like screen layouts or print pages?
Yes — aspect ratios apply anywhere two dimensions matter. For CSS grid columns, plug in column-width and row-height to find when your grid is on a clean ratio. For print, US Letter is 8.5x11 (17:22), A4 is 210x297 (which simplifies via the irrational sqrt(2) to roughly 1:1.414). Furniture, displays, paintings, and even font character widths can be checked against known ratios this way.
What does 'the golden ratio' have to do with aspect ratio?
The golden ratio is approximately 1.618:1, often cited in art and architecture for visually pleasing proportions. It appears in nature (nautilus shells, sunflower seed spirals) and was used by Renaissance painters. As an image aspect it sits between 16:10 (1.6:1) and 5:3 (1.667:1), so any of those are 'close enough' for a design context. Pure 1.618 is irrational, so it cannot be expressed as a clean integer ratio.
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