The short version
Divide width and height by their greatest common divisor. For 1920 × 1080, the greatest common divisor is 120, so the simplified aspect ratio is 16:9.
What matters most
- Use the original pixel dimensions when possible.
- A decimal value helps compare nearly matching ratios.
- Some display labels such as 21:9 are marketing families rather than exact ratios.
How to apply it
- Record width first and height second.
- Find the greatest whole number that divides both dimensions.
- Divide both values by that number.
- If the result is unwieldy, calculate width ÷ height and report an approximate familiar ratio.
Reference table
| Dimensions | Calculation | Result |
|---|---|---|
| 1920 × 1080 | ÷ 120 | 16:9 |
| 1080 × 1350 | ÷ 270 | 4:5 |
| 3000 × 2000 | ÷ 1000 | 3:2 |
| 1366 × 768 | ÷ 2 | 683:384, approximately 16:9 |
Use exact dimensions and units in production notes; familiar labels can describe more than one standard.
Common mistakes to avoid
- Dividing only one dimension.
- Rounding too early and treating a near match as exact.
- Using file size or megapixels instead of width and height.
Continue with the right tool
Use a calculator to check the numbers against your own source and destination instead of relying on a generic preset.
Related guides
What Is Aspect Ratio? A Practical Guide to Image and Video Shape
Understand aspect ratio, how width and height form a ratio, why it differs from resolution, and how to choose the right shape for images and video.
Aspect ratio basicsHow to Change Aspect Ratio Without Ruining the Composition
Choose between crop, padding and reframing when changing an image or video aspect ratio, with a practical decision process.
Aspect ratio basicsHow to Change Aspect Ratio Without Cropping
Keep every part of an image or video visible by adding canvas space, letterboxing or designing an adaptive background.
Frequently asked questions
Why does 1366 × 768 not simplify to 16:9?
Its exact ratio is 683:384. It is only about 0.05% wider than 16:9, so it is commonly grouped with that family.
Should units be pixels?
No, but both values must use the same unit. Inches, centimeters and pixels all work.
Can I find ratio from megapixels alone?
No. Total pixel count does not reveal how those pixels are split between width and height.