What is an aspect ratio?
Aspect ratio expresses the proportion of width to height. It’s written like 16:9 or 4:5. If you resize while keeping proportions, the ratio stays unchanged—only the pixel count and sharpness (PPI/DPI) change.
Popular aspect ratios
| Ratio | Typical use | Example dimensions |
|---|---|---|
| 1:1 | Square posts | 1080×1080 |
| 3:2 | DSLR photos / prints | 3000×2000 |
| 4:3 | Tablets / classic TV | 2048×1536 |
| 16:9 | HD/4K video, YouTube | 1920×1080 |
| 9:16 | Vertical Reels/TikTok | 1080×1920 |
| 4:5 | IG portrait feed | 1080×1350 |
| 21:9 | Ultrawide / cinema | 3440×1440 |
How the calculator works
- Simplify ratio: divide width and height by their GCD (greatest common divisor): ratio = (w÷g) : (h÷g).
- Solve missing side: for a target ratio R = a:b, if you provide width we do height = width × b ÷ a (and vice-versa).
- Common sizes: quickly list HD, FHD, QHD, 4K/8K, ultrawide, and DCI formats with simplified ratios.
Best practices for design, print & video
- Keep ratios consistent across design → export → upload to avoid letterboxing or unexpected cropping.
- Plan for platform rules: square (1:1) for feeds, 4:5 for tall portrait, 9:16 for stories/reels, 16:9 for YouTube.
- Print prep: pick inch sizes first (e.g., 8×10, 11×14) then convert to pixels at 300–350 DPI for sharp output.
Quick formulas
GCD simplification → ratio = (W ÷ GCD) : (H ÷ GCD)
Solve side (a:b): height = width × b ÷ a; width = height × a ÷ b
FAQs
Does resizing change the aspect ratio?
No, as long as width and height are scaled proportionally.
What’s the easiest ratio for social media?
Square (1:1) is universal. Use 4:5 for portrait feeds and 9:16 for stories/reels.
Can I enter large values?
Yes—works for any integer widths/heights. The math uses the greatest common divisor for accuracy.