Aspect Ratio CalculatorCalculators
Aspect ratio of a size, or the missing side from a ratio.
How to calculate 16:9 dimensions for any width or height
A 16:9 frame is 16 units wide for every 9 units high. Work out the missing side, then crop the image to that shape instead of stretching it.
What goes wrong when the ratio is off
A video, slide, or thumbnail with the wrong ratio gets fixed by whatever shows it. A player adds black bars, a page stretches the picture, or an app crops the top off a head. 1920 × 1080, 1280 × 720, and 3840 × 2160 are all 16:9, so each one fills a widescreen frame. 1440 × 900 is 16:10, and most phone photos are 4:3, so both leave bars or get cropped.
The arithmetic is short but easy to fumble under a deadline: height = width × 9 ÷ 16, so 1280 pixels wide gives 720 high. Resizing a 4:3 photo to those numbers without cropping it first squashes everything in the picture.
Find the size, then crop to it
The Aspect Ratio Calculator works both ways. Ratio from a size reduces a width and height by their greatest common divisor: 1920 × 1080 becomes 16:9, and 2560 × 1080 is exactly 64:27, the size sold as 21:9 ultrawide. Missing side from a ratio takes a preset such as 16:9, 4:3, or 21:9 and the side you know, and returns the other side. When the answer isn't a whole number of pixels, the rounded size is shown too.
To turn an existing image into 16:9, use the Image Cropper. Set the aspect ratio to 16:9 and the crop box keeps that shape while you move and resize it, or type X, Y, Width, and Height in the image's own pixels. From a 4000 × 3000 photo, the full-width 16:9 crop is 4000 × 2250. The kept pixels are copied one for one, so cropping doesn't soften the image. It only crops; scaling the result to 1280 × 720 is a separate step.
Make an image 16:9 at the size you need
- Open the Aspect Ratio Calculator and choose Missing side from a ratio.
- Pick 16:9 and enter the width you need, for example 1280, to get the height, 720.
- Open the Image Cropper, load the image, and set Aspect ratio to 16:9.
- Move the box over the part of the picture you want to keep, or type its X and Y position.
- Choose the output format and press Crop and download.
- Resize the cropped image to the width and height from step 2.
What the calculator and cropper won't do
- A side worked out from a ratio may not be a whole number of pixels. The calculator shows the rounded size.
- The Image Cropper handles one image at a time, in rectangles only.
- Cropping removes part of the picture. If nothing can be cut, the image needs bars or a background instead.
- Animated GIF and WebP files give a still crop of the first frame.
Frequently asked questions
What is the height of 16:9 at 1920 wide?
1080 pixels: 1920 × 9 ÷ 16.
What ratio is 2560 × 1080?
Exactly 64:27, which is sold as 21:9 ultrawide.
How do I change a 4:3 photo to 16:9?
Crop it with the ratio locked to 16:9. From a 4000 × 3000 photo the full-width crop is 4000 × 2250. Stretching it instead distorts the picture.
Does cropping lower image quality?
No. The kept pixels are copied exactly. Only JPG output is saved again, at quality 95.
Related tools
Tools used in this guide
Image CropperImage Tools
Crops images with a draggable box, aspect ratio presets, and exact pixel fields.
