Aspect ratio calculator
Resize while keeping proportions and find the simplified ratio (like 16:9) — in your browser.
Runs 100% in your browserAspect ratio: —
How to calculate aspect ratio
- Enter the original size. Type the original width and height to lock the ratio.
- Change one dimension. Enter a new width or height; the other is calculated.
- Use the result. Read the matching dimension and the simplified ratio.
About aspect ratios
An aspect ratio is the proportional relationship between width and height. Keeping it constant when you resize prevents stretching or letterboxing — essential for video exports, responsive images, thumbnails and print. Lock your source dimensions, change one side, and this calculator gives the other instantly, plus the lowest-terms ratio so you can confirm you are matching a standard like 16:9 or 4:3.
Frequently asked questions
- Enter your original width and height to set the ratio, then change either the new width or new height — the tool fills in the other dimension so the proportions stay identical.
- It reduces your width:height to lowest terms using the greatest common divisor — for example 1920×1080 simplifies to 16:9.
- 16:9 (HD video and most screens), 4:3 (legacy displays), 1:1 (square / social posts), 21:9 (ultrawide), 3:2 (photography) and 9:16 (vertical / stories).
- Yes — dimensions can be fractional, and results are rounded to two decimals where needed.