Image Aspect Ratio Calculator
Enter pixel width and height to get the simplified aspect ratio (via GCD reduction), the decimal ratio, and the closest standard ratio like 16:9 or 4:3. Runs in your browser.
Aspect ratio
- Simplified ratio
- 16:9
- Decimal ratio
- 1.7778
- Greatest common divisor
- 120
- Closest standard ratio
- 16:9 (widescreen HD)
About this tool
The aspect ratio of an image or screen is the relationship between its width and its height, written as two numbers like 16:9. This calculator takes any pixel width and height and reduces them to their simplest whole-number ratio using the greatest common divisor (GCD) — so 1920×1080 becomes 16:9 and 1280×1024 becomes 5:4 — and also reports the exact decimal ratio and the nearest well-known standard. Knowing the ratio matters when you crop or resize without distortion, choose a video resolution, design responsive layouts, or pick the right canvas for a platform (16:9 for YouTube, 9:16 for stories and reels, 1:1 for many social posts). The math is exact integer arithmetic done entirely in your browser; nothing is uploaded.
How to use it
- Enter the width in pixels.
- Enter the height in pixels.
- Read the simplified ratio, the decimal ratio, and the closest standard ratio.
- Copy the results to share or document.
Frequently asked questions
- How is the simplified ratio calculated?
- The width and height are divided by their greatest common divisor (GCD). For 1920×1080 the GCD is 120, so dividing both gives 16:9. This is the same reduction used to simplify any fraction to lowest terms.
- Why does my ratio not match a common name like 16:9?
- Either the dimensions genuinely use a non-standard ratio, or rounding in the original size shifted it slightly. The tool flags the closest standard ratio only when the decimal is within about 1% of it; otherwise it reports the exact reduced ratio.
- What is the difference between the ratio and the decimal ratio?
- The ratio (16:9) expresses the shape as two whole numbers; the decimal ratio (1.7778) is width divided by height. The decimal is handy for comparing two near-identical shapes or for CSS where a single number is easier to use.
- Does aspect ratio depend on resolution?
- No — 1280×720 and 1920×1080 are both 16:9 despite different pixel counts. Aspect ratio describes shape, not size or sharpness. Two images with the same ratio scale to each other without cropping or stretching.
- Which ratios are most common?
- 16:9 for HD video and most monitors, 9:16 for vertical phone video and stories, 1:1 for square social posts, 4:3 for older displays and many cameras, 3:2 for 35mm-style photography, and 21:9 for ultrawide.
- Is anything uploaded?
- No. Only the two numbers you type are used, and all calculation happens in your browser with no network request.