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Aspect ratio is the proportional relationship between a width and a height — 16:9 for most videos, 4:3 for old TVs, 1:1 for a square post. Knowing the ratio of a set of dimensions matters whenever you resize an image, choose a screen, or design to a standard format without distorting it.
Enter a width and a height, and the simplified aspect ratio plus the decimal ratio appear at once.
Aspect Ratio Calculator: step-by-step worked example
- Width
- 3,440
- Height
- 1,440
- 1
Round to whole pixels
W = round(width), H = round(height)
= 3,440 × 1,440
- 2
GCD (Euclid's algorithm)
GCD(a, b) = GCD(b, a mod b) — until the remainder is 0
3440 mod 1440 = 560 → 1440 mod 560 = 320 → 560 mod 320 = 240 → 320 mod 240 = 80 → 240 mod 80 = 0 = 80
- 3
Divide both sides by the GCD
Ratio = (W ÷ GCD) : (H ÷ GCD)
3440 ÷ 80 : 1440 ÷ 80 = 43:18
- 4
Decimal ratio
Width ÷ Height (4 decimals)
3,440 ÷ 1,440 = 2.3889
- 4:31.3333
- 3:21.5
- 16:101.6
- 16:91.7778
- 21:92.3333
- 43:18 ★2.3889
Good to know: Marketing names like "21:9" are rounded labels: 3440×1440 is really 43:18 (2.39) and 2560×1080 is 64:27 (2.37). When cropping, matching the decimal ratio is what counts.
Aspect Ratio Calculator — how it works
How it's found
The aspect ratio is the width and height reduced to their simplest whole-number form by dividing both by their greatest common divisor (GCD). 1920 and 1080 share a GCD of 120, so 1920:1080 simplifies to 16:9.
Common aspect ratios
| Ratio | Used for |
|---|---|
| 16:9 | HD/4K video, most modern screens |
| 4:3 | old TVs and monitors, some cameras |
| 1:1 | square social posts (Instagram) |
| 21:9 | ultrawide monitors, cinema |
| 3:2 | classic photography, many prints |
| 9:16 | vertical video (Stories, Reels, TikTok) |
Why it matters
To resize without distortion, the new dimensions must keep the same ratio. If an image is 1600×900 (16:9) and you set the width to 800, the height must be 450 to stay 16:9 — otherwise it stretches. The ratio (and its decimal form, 1.778 for 16:9) is what you hold constant.
Where it helps
- Resizing images or video without stretching
- Choosing a screen or export format
- Designing to a platform's required ratio (thumbnails, ads, stories)
Worked example
A Full HD screen is 1920×1080. The greatest common divisor of 1920 and 1080 is 120, so dividing both gives 1920÷120 : 1080÷120 = 16:9 — the standard widescreen ratio, with a decimal value of 1.778. Compare an older 1280×1024 monitor: its GCD is 256, giving 5:4 (decimal 1.25), which is why 4:3 content looked slightly stretched on those screens. Knowing the ratio lets you resize safely: to shrink the 1920×1080 image to 1280 wide, keep 16:9 and the height becomes 1280 ÷ (16/9) = 720.
Frequently asked questions
How do I calculate an aspect ratio?+
Divide the width and height by their greatest common divisor to reduce them to simplest form. 1920×1080 has a GCD of 120, giving 16:9. The tool does this instantly.
What is 1920×1080 as an aspect ratio?+
16:9, the standard widescreen ratio (decimal 1.778). It's used for HD and 4K video and most modern displays.
How do I resize an image without distorting it?+
Keep the same aspect ratio. If the original is 16:9 and you set a new width, multiply by 9/16 for the height (or divide the width by 1.778). Changing only one dimension stretches the image.
What is the aspect ratio of a vertical video?+
9:16 — the portrait version of 16:9, used for Stories, Reels and TikTok. A 1080×1920 frame is 9:16.
What does the decimal ratio mean?+
It's the width divided by the height: 16:9 is 1.778, 4:3 is 1.333, 1:1 is 1.0. The decimal is handy for quick resize maths and comparing formats.
Why did 4:3 content look stretched on old monitors?+
Many old monitors were 5:4 (1280×1024), slightly taller than 4:3 (1.25 vs 1.333). Displaying 4:3 content full-screen stretched it a little to fit.
About this page
- Publisher:
- Kalkoro — Teknolojig Bilişim Teknolojileri A.Ş., İstanbul
- Written by:
- Ahmet Tur — Editor (Math, date & time, unit conversion, physics & chemistry, everyday tools)
- Reviewed by:
- Kübra Yıldız — Editor
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