Enter a width and height to see the reduced aspect ratio (for example 16 : 9).
Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
This tool runs in your browser. Your calculator inputs and results are never transmitted to us or to ad/affiliate partners. Ads and sponsored links may set third-party cookies to serve and measure them, but they never receive your calculation values. If you explicitly save a scenario, its permitted fields stay in local browser storage until you clear them. See our Privacy Policy.
Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
What does this calculator estimate?
An aspect ratio calculator reduces a width and height to the simplest ratio. Enter the dimensions to see the ratio (like 16:9) and decimal value.
- Ratio = width:height reduced by gcd
- 1920×1080 = 16:9
- Used for screens, video, and images
What aspect ratios are for
Aspect ratio describes the proportional shape of a screen or image — 16:9 widescreen, 4:3 classic, 1:1 square. Knowing it matters for video delivery, image cropping, and responsive design.
Limitations to watch for
The ratio describes shape, not size — a 320×180 image and a 1920×1080 video are both 16:9. Non-integer ratios (like 1.91:1 for some social ads) round to whole numbers; the decimal value shows the exact proportion.
How to use it in practice
Enter your canvas or media dimensions to find the ratio. Use it to match deliverables to platform specs: YouTube 16:9, TikTok 9:16, Instagram 1:1 or 4:5. Scale dimensions while preserving the ratio by multiplying both sides by the same factor.
['Enter the width and height in pixels (or any unit).', 'Read the reduced ratio and decimal value.', "Match it to the platform's spec."]
How this calculator works
Formula
Aspect ratio = width ÷ height reduced to the smallest whole-number ratio using the greatest common divisor (gcd). The tool also reports the decimal value.
Worked example
1920×1080 divides by gcd 120 → 16:9, the standard widescreen ratio.
Assumptions to verify
- Width and height are positive numbers.
- The gcd reduction produces the standard form.
- The decimal value reflects the exact proportion.
Frequently asked questions
What is an aspect ratio?
The proportional relationship between width and height: 1920×1080 reduced to 16:9 means 16 units wide for every 9 tall.
How do I calculate it?
Divide both dimensions by their greatest common divisor. 1920÷120 = 16, 1080÷120 = 9 → 16:9.
What is 16:9 used for?
Standard widescreen — TVs, YouTube, most video. 9:16 is vertical video (TikTok, Shorts); 1:1 is square (Instagram).
What's the difference between ratio and resolution?
Ratio is the shape; resolution is the pixel count. 320×180 and 1920×1080 are both 16:9 at different resolutions.
How do I scale while keeping the ratio?
Multiply both dimensions by the same factor — or in the resizer, use the 'inside' fit which preserves the ratio.
What is a non-integer ratio?
Some formats use ratios like 1.91:1 (Facebook feed) that don't reduce to small whole numbers — the decimal value shows it.
Does orientation matter?
Yes — 16:9 is landscape, 9:16 is portrait. Rotating swaps the sides.
Cite this tool
BoringToolsKit. “Aspect Ratio Calculator.” boringtoolskit.com/aspect-ratio-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.