Calculate aspect ratio from width and height, find a missing dimension from a known ratio, or proportionally scale any rectangle. Includes presets for 16:9, 4:3, 21:9, 9:16, 1:1, cinematic, A4, and golden ratio.
Enter width and height in any unit (pixels, inches, mm). We simplify the ratio using the greatest common divisor.
Aspect ratio
Pick a preset ratio (or type your own), enter one dimension, and we compute the other.
Width is known; height is computed from the ratio.
Result dimensions
Enter the original width and height, then change one of the new dimensions — the other will follow the same proportion.
Editing new width; height follows the original proportion.
Scaled dimensions
Common resolutions
Click a row to load it into the active mode.
Name
Width × Height
Ratio
FAQ
What is an aspect ratio?
Aspect ratio is the proportion between width and height of a rectangle — a photo, video frame, screen, page, or social post. It is written as W:H, so a 1920×1080 image has a 16:9 ratio. Two images with the same ratio look identical in shape, even if their pixel count differs.
16:9 vs 9:16 — when do I use each?
16:9 is horizontal and used for YouTube, TVs, desktop monitors, most video players, and cinema prosumer cameras. 9:16 is the same shape rotated 90°, used for phone-first video formats like TikTok, Instagram Reels, YouTube Shorts, and Stories. Pick the one that matches where your content will be watched.
How is the ratio simplified?
For whole-number dimensions, we divide both numbers by their greatest common divisor (GCD). Example: 1920 and 1080 share a GCD of 120, so 1920÷120 = 16 and 1080÷120 = 9 — the ratio is 16:9. If the numbers are decimals or the GCD gives an ugly result, we also show the decimal form such as 1.78:1.
What is the difference between scaling and cropping?
Scaling keeps the full image but changes its size — both width and height shrink or grow together, so the ratio stays the same. Cropping cuts pixels from the edges to change the ratio, which changes what the viewer sees. This calculator handles scaling (proportional resizing); cropping needs to be done in an editor.
Which ratio should I pick for Instagram, YouTube, TikTok, or cinema?
Instagram feed: 1:1 (square) or 4:5 portrait. Instagram Stories/Reels and TikTok: 9:16 vertical. Standard YouTube: 16:9. YouTube Shorts: 9:16. Ultrawide cinematic: 2.35:1 or 2.39:1. Classic Hollywood: 1.85:1. Older TV or tablet content: 4:3.
What are the golden and A4 ratios about?
The golden ratio (≈ 1:1.618) is a classic proportion used in art, photography composition, and UI layout because it is considered visually pleasing. The A4 ratio (1:√2 ≈ 1:1.414) is special because halving an A4 sheet along its long edge gives two sheets of the same ratio — that is why the ISO 216 paper series works.
Results are for design and layout guidance. Verify with your camera, editor, or delivery platform specs before final export.
The Aspect Ratio Calculator converts between image, video, and screen dimensions and their ratio expression. It works in three modes. In Ratio mode, enter width and height in any unit and the tool returns the simplified integer ratio (using the greatest common divisor) plus a decimal form. Example: 1920 and 1080 give 16:9 (or 1.78:1).
In Dimensions mode, choose a preset ratio such as 16:9, 4:3, 21:9, 32:9, 1:1, 3:2, 5:4, 9:16, 2.35:1, A4 (1:1.414), or the golden ratio (1:1.618), then type one side and the other is computed automatically. In Scale mode, enter the original width and height and a new width — the tool returns the matching height that preserves the original proportion, plus the scale percentage.
A live SVG preview shows the rectangle in real time, and a common-resolutions table lists 720p, 1080p, 4K, ultrawide, and social media formats for quick reference.