How this calculator works
Aspect ratio is the proportional relationship between a shape's width and height, written as two numbers separated by a colon. This calculator simplifies any width and height pair to its lowest-terms ratio and decimal value, and — in the second mode — takes a known ratio plus a new width and solves for the height that keeps the proportions identical.
Photos, videos, monitors and phone screens are all built around a handful of standard ratios. The reference table below shows the most common ones so you can see at a glance which family your numbers belong to.
The formulas
Simplified ratio: divide width and height by their greatest common factor (GCF)Decimal ratio: width ÷ heightScaling to a new width: new height = new width × (original height ÷ original width)Scaling preserves the decimal ratio exactly — only the simplified whole-number form and the pixel dimensions change.
Worked example: scaling 16:9 to a 2,560-pixel-wide display
- Start from the standard 16:9 ratio (16 wide for every 9 tall).
- You want a display 2,560 pixels wide and need the matching height.
- New height = 2,560 × 9 ÷ 16 = 1,440 pixels.
- The result, 2,560×1,440, is itself a well-known standard resolution (QHD), confirming the ratio held.
Frequently asked questions
How do I simplify a resolution like 1920×1080 by hand?
Find the greatest common factor of both numbers (120, in this case) and divide each by it: 1920 ÷ 120 = 16, 1080 ÷ 120 = 9, giving 16:9.
What is the difference between 16:9 and 16:10?
16:10 is taller relative to its width than 16:9 (a decimal ratio of 1.6 versus 1.778). 16:10 was common on older laptop and monitor panels; 16:9 has been the near-universal standard for HDTV, streaming video and most monitors since the HD era.
Why is 21:9 called 'ultrawide' when the simplified ratio isn't exactly 21:9?
Most ultrawide monitors are actually close to 64:27 (≈2.370) or 43:18 (≈2.389), not the exact 21:9 (≈2.333) the marketing name suggests. 'Ultrawide' has become a category name more than a literal ratio.
Does aspect ratio affect image quality?
Not directly — ratio is about shape, not sharpness. But stretching an image to a different ratio without cropping will distort it, since width and height no longer scale together.
What height keeps a 4:3 ratio at 1200 pixels wide?
900 pixels. A 4:3 ratio means height is three-quarters of width, so 1200 × 3 ÷ 4 = 900. This follows the same scaling rule used throughout this calculator — new height = new width × (original height ÷ original width) — where 3 ÷ 4 = 0.75, and 1200 × 0.75 = 900.