Aspect Ratio Calculator
Calculate proportions, resize video and image dimensions without distortion, and determine exact aspect ratios with live visual feedback.
16:9
Understanding Video & Display Aspect Ratios
Aspect ratio expresses the proportional relationship between a visual medium's width and height. It is represented as two numbers separated by a colon (W:H), regardless of the actual physical size or resolution in pixels.
The Mathematical Formula
The cross-multiplication formula guarantees pixel-perfect scaling without letterboxing or squashing:
How Aspect Ratio Math Works
An aspect ratio is the proportional relationship between width and height, written width:height. To reduce any resolution to its simplest ratio, divide both numbers by their greatest common divisor (GCD). For 1920x1080, GCD(1920, 1080) = 120, so 1920/120 : 1080/120 = 16:9.
| Ratio | Decimal | Common uses | Example resolution |
|---|---|---|---|
| 16:9 | 1.78 | TV, YouTube, monitors | 1920x1080 (Full HD) |
| 16:10 | 1.60 | Laptop displays | 1920x1200 |
| 4:3 | 1.33 | Classic TV, iPad | 2048x1536 |
| 3:2 | 1.50 | DSLR photos, Surface | 3000x2000 |
| 1:1 | 1.00 | Instagram posts | 1080x1080 |
| 4:5 | 0.80 | Instagram portrait | 1080x1350 |
| 9:16 | 0.56 | Reels, Shorts, TikTok | 1080x1920 |
| 21:9 | 2.33 | Ultrawide monitors | 3440x1440 |
16:9 Resolution Reference
The 16:9 family dominates video. Every step up multiplies each dimension, keeping the ratio identical:
| Label | Resolution | Total pixels |
|---|---|---|
| 720p (HD) | 1280 x 720 | 921,600 |
| 1080p (Full HD) | 1920 x 1080 | 2,073,600 |
| 1440p (QHD) | 2560 x 1440 | 3,686,400 |
| 2160p (4K UHD) | 3840 x 2160 | 8,294,400 |
| 4320p (8K UHD) | 7680 x 4320 | 33,177,600 |
Worked Examples
Tip: when cropping photos, lock the ratio first. A 3:2 photo cropped to 16:9 for a video thumbnail loses the top and bottom; compose with that in mind when shooting.
Frequently Asked Questions
How do you calculate aspect ratio?
Divide width and height by their greatest common divisor. For 1920x1080, GCD(1920,1080) = 120, giving 16:9. This calculator does the reduction automatically.
What is the aspect ratio of 1920x1080?
16:9. Both numbers divide evenly by 120: 1920/120 = 16 and 1080/120 = 9.
What aspect ratio is 1080x1920?
9:16, the vertical video ratio used by TikTok, Reels and YouTube Shorts. It is 16:9 rotated 90 degrees.
How do I find the missing height for a 16:9 video?
Multiply the width by 9/16. For width 1280: 1280 x 9 / 16 = 720. For width 3840: 3840 x 9 / 16 = 2160.
What is the difference between 16:9 and 16:10?
16:9 (1.78) is the video standard; 16:10 (1.60) is slightly taller and common on productivity laptops like MacBooks, giving extra vertical room for documents.
What resolution is 4K?
3840x2160, marketed as 4K UHD. It has exactly 4 times the pixels of 1080p: 8,294,400 vs 2,073,600.
Why do movies have black bars?
Cinema ratios like 2.39:1 are wider than 16:9 screens, so letterbox bars fill the unused top and bottom. Cropping the film instead would cut off the sides of the image.
What aspect ratio should I use for Instagram?
1:1 square (1080x1080) for feed posts, 4:5 portrait (1080x1350) for maximum feed space, and 9:16 (1080x1920) for Reels and Stories.
How do I convert 4:3 to 16:9?
You cannot convert without cropping or stretching: 4:3 (1.33) is narrower than 16:9 (1.78). Either crop top and bottom, pillarbox with side bars, or stretch (which distorts).
What is pixel aspect ratio vs display aspect ratio?
Display aspect ratio is the image shape (16:9). Pixel aspect ratio is the shape of individual pixels, almost always 1:1 (square) today; older broadcast video used non-square pixels.
What is the GCD method for simplifying ratios?
Find the greatest common divisor of both numbers and divide each by it. GCD(1920,1080) = 120 gives 16:9. Euclid's algorithm computes GCD fast even for huge numbers.
Does aspect ratio affect file size?
Only indirectly through pixel count. A 1920x1080 image and a 1080x1080 image at the same compression have sizes proportional to their pixel counts: 2,073,600 vs 1,166,400.
What aspect ratio is an iPhone photo?
iPhone cameras shoot 4:3 by default (4032x3024 on recent models), switchable to 16:9 or 1:1 in the camera app.
What is 21:9 used for?
Ultrawide gaming and productivity monitors (e.g. 3440x1440). It shows roughly a third more horizontal content than 16:9, great for timelines and side-by-side windows.
Is this aspect ratio calculator free?
Yes. Compute ratios, scale dimensions and simplify resolutions instantly in your browser with no account.
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