DIMENSIONS
Aspect Ratio Calculator
Convert between width, height, and aspect ratio — with common presets.
RATIO MATH
Find a ratio or dimensions
Aspect ratio guide
An aspect ratio is the proportional relationship between width and height — 16:9, 4:3, 21:9 — and it is the first decision in any screen, video, or game design. This calculator finds the ratio of any width and height, or computes missing dimensions from a ratio, with the common presets one click away.
It runs entirely in your browser: enter two dimensions to find the ratio, or pick a ratio and a base dimension to get the matching size.
The standard ratios and where they live
Each ratio is a product of its medium’s history:
- 16:9 — the modern widescreen standard: TVs, monitors, YouTube, and most games.
- 4:3 — classic television and early computer monitors; still common in photography and retro games.
- 21:9 — ultrawide monitors and cinematic formats.
- 3:2 — classic 35mm photography (APS-C sensors).
- 1:1 — square: social media profile pictures and Instagram posts.
- 9:16 — vertical video: TikTok, Reels, and Shorts.
How the math works
The ratio is width ÷ height simplified to the smallest whole numbers. 1920 ÷ 1080 = 1.777…, and dividing both by their greatest common divisor (120) gives 16:9.
Going the other way: with a 16:9 ratio and a 1280px width, the height is 1280 × 9 ÷ 16 = 720px. The calculator does both directions and rounds sensibly for the dimension mode.
Why ratio discipline matters
Mixing aspect ratios is how images get cropped, videos get letterboxed, and UIs break. In game development, the camera and UI must adapt to every player’s screen — 16:9, 21:9, 4:3, and handheld verticals. Knowing the ratio you are targeting (and the safe area inside it) prevents cut-off HUD elements and stretched sprites.
For web and video, the ratio determines resolution tiers: 1080p, 1440p, and 4K are all 16:9, while "4K ultrawide" is 21:9 at 3840×1600.
Frequently asked questions
What is an aspect ratio?
The proportional width-to-height relationship of a screen or image, expressed as two numbers like 16:9. It is independent of absolute size.
How do I calculate an aspect ratio?
Divide width and height by their greatest common divisor. 1920×1080 ÷ 120 = 16:9.
What is the difference between 16:9 and 4:3?
16:9 is widescreen (nearly twice as wide as tall); 4:3 is the older, more square standard. Content designed for one will letterbox or crop on the other.
How do I find the height from a ratio and width?
height = width × ratioH ÷ ratioW. At 16:9 with width 1280: 1280 × 9 ÷ 16 = 720.
Is 1920×1080 the same ratio as 3840×2160?
Yes — both are 16:9. The ratio is the same; only the resolution (pixel count) differs.
Privacy note: ratio and dimension calculations happen in your browser. Nothing is uploaded.