1920x1080 reduces to 16:9
Dividing both numbers by their greatest common divisor, 120, gives 16 and 9 — the standard widescreen ratio.
Aspect ratio calculator
To find an aspect ratio, enter the width and height in pixels and the calculator divides both by their largest common divisor: 1920 by 1080 becomes 16:9, and 1080 by 1350 becomes 4:5. It also names the nearest standard ratio, and presets fill in common social media sizes in one click.
Calculate an aspect ratio
Common presets
16:9
Simplified by dividing both dimensions by their greatest common divisor, 120.
- Decimal ratio
- 1.7778
- Closest common ratio
- 16:9 (exact)
Formula
ratio = width ÷ gcd(width, height) : height ÷ gcd(width, height)
What aspect ratio does each social network recommend?
Vertical 9:16 for full-screen video, 1:1 or 4:5 for feed images, and 16:9 for landscape video cover most networks. These are the ratios SkedCast’s composer checks media against for each platform:
| Platform | Images | Video |
|---|---|---|
| X (Twitter) | 16:9, 1:1 | 16:9, 9:16, 1:1 |
| 1:1, 4:5, 1.91:1 | 16:9, 1:1, 9:16 | |
| 1:1, 4:5, 1.91:1 | 9:16 | |
| Facebook Pages | 1:1, 4:5, 1.91:1 | 16:9, 9:16, 1:1 |
| TikTok | 9:16 | 9:16, 1:1, 16:9 |
| YouTube | No images | 16:9, 9:16 |
| Threads | 1:1, 4:5 | 9:16 |
| 2:3 | 2:3, 9:16, 1:1 | |
| Bluesky | 1:1, 4:5, 16:9, 1.91:1 | 9:16, 16:9, 1:1 |
| Telegram | Any | Any |
| Google Business Profile | 1:1, 4:3 | No video |
For exact pixel sizes on each network, see the media spec checker.
How do you calculate an aspect ratio by hand?
Find the largest number that divides both the width and the height, then divide each by it. For 1920 by 1080, that number is 120: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the ratio is 16:9. To find a height for a ratio, multiply the width by the ratio’s second number and divide by the first: a 1080-pixel-wide 4:5 image is 1080 × 5 ÷ 4 = 1350 pixels tall.
How do you use the aspect ratio calculator?
- Enter your width and height in pixels. Type the exact pixel dimensions of your image or video export.
- Or click a common preset. Presets like Full HD, square and vertical Reel sizes fill both fields for you in one click.
- Read the simplified ratio. The result shows your dimensions reduced to their lowest terms, plus the divisor used to get there.
- Compare against the closest common ratio. The result also names the nearest standard ratio, like 16:9 or 4:5, and whether your input matches it exactly.
- Re-export if your ratio does not match your target platform. A mismatched ratio often means a platform will crop your media rather than resize it evenly.
What does it look like in practice?
1080x1350 reduces to 4:5
Dividing both numbers by their greatest common divisor, 270, gives 4 and 5 — a common Instagram portrait ratio.
How do you make an image fit a platform’s ratio?
Crop or pad it to the ratio before you upload, with the important part in the middle so a platform’s own crop does not cut it off. The image resizer does this in the browser, and SkedCast checks each file against the platform’s media rules while you build the post.
Aspect ratio calculator FAQ
- How is the aspect ratio calculated?
- Both the width and height are divided by their greatest common divisor, found using the Euclidean algorithm, to reach the smallest whole-number ratio.
- Why does 1920x1080 become 16:9 instead of some other ratio?
- Because 120 is the largest number that divides evenly into both 1920 and 1080, and dividing both by it gives exactly 16 and 9.
- What if my dimensions do not match a common ratio exactly?
- The calculator still simplifies them precisely and separately names the closest common ratio, so you can see how far off you are.
- Does this tool resize or crop my actual image?
- No — it only calculates the ratio from the numbers you type in; no file is uploaded or modified.
- What aspect ratio should I use for a Reel or Short?
- A vertical 9:16 ratio, commonly 1080 by 1920 pixels, is the standard export size for Reels, TikTok and Shorts.
- Does the calculator store or send my dimensions anywhere?
- No — the calculation happens entirely in your browser as you type, and nothing is uploaded or saved.
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