Aspect Ratio Calculator — Free Online Tool

Resize keeping ratio

Enter your original size, then type a new width or height — the other value is filled in to keep the same proportions.

Original size

Original width

Original height

New size

New width

New height

Round the calculated dimension to whole pixels

Resized dimensions

Free online aspect ratio calculator

This aspect ratio calculator does two jobs in one place. Use Resize keeping ratio to scale an image or video to a new width or height without distorting it, and use Simplify a ratio to turn raw pixel dimensions like 1920 × 1080 into a clean ratio such as 16:9. Everything updates live as you type and runs privately in your browser — no uploads, no sign-up, and no data ever leaves your device.

How to resize while keeping the aspect ratio

Type your original width and original height into the first card.
Enter the new width you want — the new height fills in automatically.
Or enter the new height instead and the matching width is calculated for you.
Whole-pixel rounding may slightly change the ratio. Turn it off for a decimal dimension, shown to 12 significant digits, then copy the resized dimensions.

How to simplify a ratio

In the second card, enter any width and height and the tool divides both by their greatest common divisor to show the simplest whole-number ratio, plus a decimal form like 1.778:1 for ratios that do not reduce neatly. Press Copy ratio to grab the simplified ratio for your notes, CSS, or a design brief. Common results include 16:9 for widescreen, 4:3 for older displays, 1:1 for square, and 3:2 for classic photos.

Private, accurate, and free

All the arithmetic happens locally in JavaScript, so your numbers stay on your machine. Need more quick math? Try our percentage calculator for discounts and changes, or convert artwork with the image to Base64 encoder. Bookmark this page so the next resize is only a click away.

Frequently asked questions

How do I keep the same aspect ratio when resizing?

Enter your original width and height, then type either the new width or the new height. The calculated dimension follows the last new dimension you edited, even when the original size changes. Whole-pixel rounding is on by default; turn it off for a decimal result shown to 12 significant digits.

What does an aspect ratio like 16:9 mean?

An aspect ratio compares width to height in the smallest whole numbers possible. 16:9 means that for every 16 units of width there are 9 units of height — the shape of most modern TVs, monitors, and video. A 1920×1080 image has exactly this ratio, which is why it simplifies to 16:9.

How is the ratio simplified?

The simplifier converts the entered decimal dimensions to exact fractions, then reduces them using their greatest common divisor. For example, 1920 × 1080 becomes 16:9, and 1.5 × 1 becomes 3:2. The decimal ratio is shown approximately; the simplified whole-number ratio preserves the entered decimals exactly.

What are common aspect ratios?

Widescreen video and displays use 16:9; older screens and many photos use 4:3; square social posts use 1:1; classic photo prints are 3:2; and ultrawide monitors and cinema often use 21:9. The simplifier will tell you which ratio your exact pixel dimensions match.

Is this calculator free and private?

Yes. Every calculation runs entirely in your browser with JavaScript, so nothing you enter is uploaded or stored. It is completely free, needs no sign-up, and keeps working offline once the page has loaded.