Aspect Ratio Calculator
Resize width and height while keeping the same aspect ratio.
Results update as you type.
About this calculator
An aspect ratio calculator keeps an image, video frame or screen in proportion when you resize it, so nothing ends up stretched or squashed. Enter the original width and height and it reduces them to the simplest whole-number ratio (like 16:9) by dividing both by their greatest common divisor. Type a new width and it returns the height that preserves the shape; type a new height instead and it returns the matching width.
Worked example: scaling a 1920×1080 image down to a 1280 width gives a height of 1280 × 1080 ÷ 1920 = 720, keeping the exact 16:9 shape. The tool also reports the ratio as a decimal (1920 ÷ 1080 = 1.778) and the original pixel count in megapixels (1920 × 1080 ÷ 1,000,000 ≈ 2.07 MP).
Photographers, video editors and web designers use it to fit an image into a fixed frame, work out crop dimensions, or check that a monitor and its content share the same ratio before letterboxing appears.
Frequently asked questions
How do I keep an image in proportion when resizing?
Divide the original width by the original height to get the ratio, then multiply your new width by (original height ÷ original width). Scaling 1920×1080 down to a 1280 width gives a height of 1280 × 1080 ÷ 1920 = 720.
What does an aspect ratio like 16:9 mean?
It is the simplified proportion of width to height. 1920:1080 both divide by 120 to give 16:9, meaning 16 units of width for every 9 of height — the standard for HD video and most monitors.
What are the most common aspect ratios?
16:9 is the standard for HD and 4K video and most monitors and phones in landscape; 4:3 is older TV and many tablets; 3:2 is common in photography and DSLR sensors; 1:1 is square (social posts); and 21:9 is ultrawide or cinematic. Entering the pixel dimensions shows which one you have.
How do I find the aspect ratio of an image?
Enter its pixel width and height as the original dimensions — the calculator divides both by their greatest common divisor to give the simplest ratio. For example 3000×2000 reduces to 3:2.
What happens if I resize without keeping the ratio?
The image distorts — circles become ovals and faces stretch. Fitting content into a frame with a different ratio instead adds black bars (letterboxing top and bottom, or pillarboxing at the sides) so the original proportion is preserved.
What does the ratio as a decimal mean?
It is width divided by height. 16:9 is 1.778 and 4:3 is 1.333 — a larger decimal means a wider, more elongated frame. It is handy when a spec is given as a single number rather than a colon ratio.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/aspect-ratio/curl
curl "https://calculator.free/api/v1/aspect-ratio/?ow=1920&oh=1080&nw=1280"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/aspect-ratio/?" + new URLSearchParams({
"ow": "1920",
"oh": "1080",
"nw": "1280"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.