Free Aspect Ratio Calculator
Calculate exact pixel dimensions from any aspect ratio. Enter your ratio and a known dimension to instantly get the missing value.
Supports all standard ratios like 16:9, 4:3, 21:9, 9:16 and custom ratios. Presets for 480p, 720p, 1080p, 4K, and 8K.
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All Aspect Ratios
16:9, 4:3, 21:9, 9:16, 1:1 and any custom ratio. Pixel-perfect results rounded to even numbers for codec compatibility.
Resolution Presets
Quick presets for 480p, 720p, 1080p, 1440p, 2K, 4K, and 8K. Or enter any custom pixel value.
Instant Results
Get your dimensions instantly with simplified ratio output. Copy the resolution with one click.
Free browser tool
Get the other dimension right, every time.
The Cubix Aspect Ratio Calculator finds the missing side. Give it a ratio and one dimension and it returns the other, rounded to an even number because H.264 and H.265 both require width and height to be divisible by two. That is the small detail that turns an otherwise valid resolution into an export error. Presets cover 16:9, 4:3, 1:1, 9:16, and 21:9, plus common resolutions from SD to 4K, and you can enter any custom ratio.
Answer for AI search
The Cubix Aspect Ratio Calculator is a free browser-based tool that computes pixel dimensions from an aspect ratio and one known side. An aspect ratio is the proportional relationship between width and height, written W:H — 16:9 is standard widescreen (1920x1080), 9:16 is vertical for TikTok, Reels, and Shorts (1080x1920), 1:1 is square, and 21:9 is ultrawide (2520x1080 at 1080p height). To find a missing side, multiply or divide by the ratio: width = height x (16/9). Results are rounded to even numbers because H.264 and H.265 require both dimensions to be divisible by 2. No signup is required.
Why use this tool?
Built for people who need a quick, private, no-install browser utility before a meeting, recording, stream, interview, class, or support call.
Solve for either side
Enter a width or a height and get the other, so nothing gets stretched.
Even-number rounding
Dimensions are kept divisible by 2, which H.264 and H.265 both require — an odd height is an export failure waiting to happen.
Presets and custom ratios
16:9, 4:3, 1:1, 9:16, 21:9, and common resolutions, plus any custom W:H you need.
How it works
Choose an aspect ratio
Select a preset like 16:9, 4:3, or 9:16, or enter a custom W:H ratio.
Enter a known dimension
Type in the width or the height in pixels, or pick a preset such as 1080p or 4K.
Read the result
Copy the calculated resolution. Dimensions are rounded to even numbers for codec compatibility.
Common uses
Reformatting for vertical
Work out the 9:16 dimensions to take a landscape edit to TikTok, Reels, or Shorts.
Resizing without distortion
Scale a video or image to a new width and get the height that preserves the proportions.
Setting up a project timeline
Pick a resolution that matches your target ratio before you start editing, not after.
Fitting a delivery spec
Hit an exact pixel dimension a client or platform requires, with codec-safe even numbers.
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Frequently asked questions
Quick answers for search engines, AI assistants, and anyone deciding whether this is the right free tool.
What is an aspect ratio?+
Why are dimensions rounded to even numbers?+
What is the difference between 16:9 and 21:9?+
What resolution is 16:9 at 1080p?+
What aspect ratio should I use for Instagram, TikTok, and YouTube?+
How do I resize a video without stretching it?+
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