Aspect Ratio Calculator

What is an aspect ratio calculator?

An aspect ratio calculator answers two everyday questions in one place: what ratio is this width × height, and what do my dimensions become if I resize while keeping that ratio. It's the quick check behind resizing a thumbnail, cropping a video, scaling a design mockup or ordering a print — any job where stretching the image is not an option.

How it works

The maths is deliberately simple:

1. Finding the ratio. Divide both sides by their greatest common divisor. 1920 × 1080 share a divisor of 120, which leaves 16:9. When the simplified numbers would be too large to be useful (1366 × 768 → 683:384), the calculator shows the decimal form instead: width ÷ height ≈ 1.779:1.
2. Resizing. The ratio is a constant — width ÷ height. To get a new height from a new width, divide by it; to get a new width from a new height, multiply. Scaling 1920 × 1080 down to a width of 1280 gives 1280 ÷ (16⁄9) = 720.

Results are rounded to whole pixels, since screens can't show half a pixel.

How to use it

1. Enter your original width and height — or tap a preset (16:9, 9:16, 4:3, 1:1, 21:9, 3:2) to start from a standard.
2. Read the aspect ratio in the headline, with the decimal version underneath.
3. To resize, type either a new width or a new height in the resize row — the other side is calculated for you on the spot.
4. Copy puts a one-line summary (original size, ratio, new size) on your clipboard.

A worked example

You have a 4000 × 3000 photo (that's 4:3) and need it 1200 pixels wide for a blog post:

• Ratio: 4000 ÷ 3000 = 1.3333
• New height: 1200 ÷ 1.3333 = 900
• Result: 1200 × 900 — same proportions, no distortion.

Need the actual file resized, not just the numbers? The Image Resizer does that right in your browser, and the Social Media Image Resizer has the platform sizes built in. For quick proportional maths in general, the Percentage Calculator is the sibling tool.

Common ratios cheat sheet

• 16:9 — YouTube, TV, most monitors (1920 × 1080, 3840 × 2160)
• 9:16 — TikTok, Reels, Shorts, phone wallpapers (1080 × 1920)
• 1:1 — square social posts (1080 × 1080)
• 4:3 — tablets, older screens, many webcams (1600 × 1200)
• 3:2 — DSLR/mirrorless photos, some laptops (6000 × 4000)
• 21:9 — ultrawide monitors, cinematic crops (2560 × 1080)

Private by design

Everything is calculated in your browser with plain JavaScript — the dimensions you type are never uploaded, stored or shared. There's no sign-up and no limit on how often you use it. More free utilities live on the all tools page.