Video Aspect Ratio Calculator
Work out any video's aspect ratio, then find the matching dimensions or the largest crop for a different target ratio.
Convert with this tool
Files stay on your device. There is no upload, no queue and no watermark, so a conversion works even with the network switched off after the page has loaded.
Supported formats & processing
| Input | Numbers you type — nothing is calculated until you change a value |
|---|---|
| Output | A live result table, recalculated on every keystroke |
| Processing | Plain arithmetic in this tab — instantaneous and offline |
About this tool
Aspect ratio mistakes cause more wasted render time than almost anything else in video work. Delivering a 4:3 file to a platform that expects 16:9 gets it letterboxed or rejected, and an odd number of pixels in either dimension will fail an H.264 encode outright.
Enter your source dimensions and this calculator reports the simplified ratio, the decimal value, the megapixel count and — most usefully — the matching height for your width at any target ratio, the matching width for your height, and the largest crop of the target shape that fits inside your frame. It also tells you how much of the frame that crop discards.
Features
- Simplifies any pair of dimensions to its lowest terms
- Matching height and matching width for any target ratio
- Largest crop of the target shape that fits your frame
- Percentage of the frame lost to that crop
- Megapixel and total pixel counts
- Seven common target ratios including 9:16 and 21:9
Frequently asked questions
Why do the dimensions need to be even numbers?
H.264 encodes in 16 × 16 macroblocks and uses chroma subsampling that halves resolution in both directions, so odd dimensions cannot be represented. Encoding an odd width is the single most common cause of a failed video export.
How do I convert 16:9 footage to 9:16 for Shorts?
Enter your source dimensions, select 9:16, and read the largest crop figure. That is the region you can use without distortion. Anything outside it has to be cropped away or replaced with a blurred background.
What is the difference between 16:9 and 1.78:1?
Nothing — they are the same ratio expressed differently. 16:9 is the fraction form and 1.78:1 is the decimal form. The calculator reports both.
Is 21:9 the same as 2.39:1?
No. 21:9 is 2.33:1, a widescreen monitor ratio. 2.39:1 is the anamorphic cinema ratio. They are close enough that both are often described as cinemascope, but they are not identical.