📐 Aspect Ratio Calculator
Simplify any width and height into its smallest whole-number ratio, then work out the missing dimension when you resize.
1. Simplify a width × height
2. Scale to a new size
📖 Common aspect ratios
| Ratio | Decimal | Where you see it |
|---|---|---|
| 1:1 | 1.000 | Square — Instagram feed, avatars, album art |
| 5:4 | 1.250 | 8×10 photo prints, some older monitors |
| 4:3 | 1.333 | Standard-definition TV, iPad, most phone photos |
| 3:2 | 1.500 | 35 mm film, most DSLR and mirrorless cameras |
| 16:10 | 1.600 | WUXGA, MacBook displays, productivity monitors |
| 16:9 | 1.778 | HD / Full HD / 4K TV, YouTube, most video |
| 2:1 | 2.000 | Univisium, some cinematic crops |
| 21:9 | 2.333 | Ultrawide monitors, anamorphic cinema |
| 9:16 | 0.563 | Vertical video — Stories, Reels, TikTok, Shorts |
How to use the Aspect Ratio Calculator
Enter a width and a height to get the ratio in simplified form, or enter a target ratio and one known dimension to solve for the missing side.
How it works
Aspect ratio is the relationship between width and height, usually written as w:h or as a decimal. It describes shape without absolute size: a 1920×1080 image and a 640×360 thumbnail share a 16:9 ratio but differ enormously in resolution. Simplifying means dividing both terms by their greatest common divisor, so 1920:1080 becomes 16:9.
When to use it
Use it when matching a crop to a platform requirement, resizing images without distortion, checking whether a design export matches the intended ratio, or choosing a screen size.
Worked example
Common resolutions reduced to their simplest ratio:
| Resolution | Ratio | Typical use |
|---|---|---|
| 1920×1080 | 16:9 | HD video, displays |
| 3840×2160 | 16:9 | 4K video |
| 1080×1080 | 1:1 | Social avatars |
| 1080×1920 | 9:16 | Vertical video |
| 2560×1440 | 16:9 | QHD display |
| 1200×630 | 1.91:1 | Open Graph preview |
Assumptions and limitations
Changing a ratio alters the shape, so a 16:9 image cropped to 1:1 loses width on both sides. Resizing to match a ratio without also specifying a target resolution can produce an unexpectedly small file. Aspect ratio does not tell you anything about pixel density or whether the source is high resolution, so check both before printing.
Frequently Asked Questions
What does an aspect ratio actually mean?
It is the proportional relationship between width and height, written as width : height. A 16:9 image is 16 units wide for every 9 units tall, so it stays the same shape whether it is 160 pixels or 3840 pixels wide. The ratio describes the shape, not the size — that is why the same ratio works for a phone screen and a cinema screen.
How do I find the missing dimension?
Multiply the known dimension by the ratio. If you know the width, height = width × (height part ÷ width part) — for 16:9 at 1920 px wide, the height is 1920 × 9 ÷ 16 = 1080 px. If you know the height instead, multiply by the inverse: width = height × (width part ÷ height part). This calculator does both directions automatically.
Does changing the aspect ratio crop or stretch the image?
It depends how you do it. Resizing a 4:3 photo to 16:9 by scaling stretches everything and squashes faces; changing the frame to 16:9 and cropping cuts off the top and bottom but keeps objects in proportion. Neither is "wrong" — use scaling when you control the source, and cropping when you must fit an existing photo into a fixed frame.
Which aspect ratio should I use for social media?
Think square-ish and vertical: 1:1 for Instagram and Facebook feed posts, 4:5 for Instagram portrait posts (it takes more vertical screen space), and 9:16 for Stories, Reels, TikTok and YouTube Shorts. For YouTube long-form and any traditional video, 16:9 remains the standard. Uploading at the platform's native ratio beats letting it crop for you.
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