Aspect Ratio Calculator
Calculate aspect ratio from width and height, simplify to standard ratios like 16:9 or 4:3, and find matching dimensions for any target width or height.
How to Use This Calculator
- Choose a mode — Find Ratio (from dimensions) or Find Dimension (scale to a target size)
- Enter your values — any positive numbers work (pixels, inches, cm, etc.)
- Click Calculate to see the simplified ratio, decimal value, and closest standard ratio
Mode
Find the Aspect Ratio
📐 How to Calculate Aspect Ratio
- Find the GCD: Find the greatest common divisor of the width and height. For 1920×1080, the GCD is 120.
- Divide both sides: 1920 ÷ 120 : 1080 ÷ 120 = 16:9.
- Decimal form: Width ÷ height = 1920 ÷ 1080 = 1.7778 — useful for comparing ratios or matching cinema formats like 2.39:1.
- Scaling to a new size: Multiply both sides by the same scale factor. To go from 1920×1080 to a 1280-wide image: 1280 ÷ 1920 = 0.667, so height = 1080 × 0.667 = 720.
🖼️ Common Aspect Ratios
Frequently Asked Questions
How do I calculate aspect ratio from width and height?
Divide both the width and height by their greatest common divisor (GCD). For 1920×1080, the GCD is 120, so 1920÷120 = 16 and 1080÷120 = 9, giving an aspect ratio of 16:9.
What is the difference between 16:9 and 4:3?
16:9 (1.78:1) is the modern widescreen standard used by HD/4K TVs, monitors, and YouTube. 4:3 (1.33:1) is the older 'fullscreen' format used by classic TVs and early computer monitors.
How do I resize an image and keep the same aspect ratio?
Enter your original width and height, then enter only your target width (or only your target height) and leave the other blank. The calculator multiplies by the same scale factor to find the missing dimension so the proportions stay identical.
What resolution is 21:9 ultrawide?
Common 21:9 (2.33:1) resolutions include 2560×1080 and 3440×1440. It's wider than 16:9 (1.78:1) and is popular for ultrawide monitors and cinematic video.
Why do my pixel dimensions not simplify to a 'clean' ratio?
Not every resolution reduces to a standard ratio like 16:9 or 4:3. For example, 1366×768 simplifies to 683:384 (roughly 1.78:1, close to but not exactly 16:9) because of how manufacturers round panel dimensions.
What's the formula for aspect ratio as a decimal?
Divide width by height. For example, 1920 ÷ 1080 = 1.7778, which is the decimal form of 16:9. This is useful for comparing ratios or matching cinema formats like 2.39:1.