There are several views of the featured image, each can have different dimensions so it is usually important to place the image focus in the center.
When the image does not fit the container around it, it is cropped either on sides or on top and bottom.
Moreover the featured image can have two layouts inside an article detail.
Following are definitions of the featured image sizes in various contexts:
Aspect ratio: 16/9 (width = 16 points, height = 9 points)
Examples:
The first position in the grid has special behaviour for desktop and mobile:
Due to the layout in the desktop view, the first article position must be slightly offset from the 16/9 aspect ratio, therefor the image has an extra few pixels at the bottom.
Examples:
The following image demonstrates the extra spaces that is needed in order to match the height of the two images next to it:
Aspect ratio: variable
Width: scales with browser width, limited to 1380px max
Height:
At the highest resolution, the image has size of 1380×600 pixels resulting in an aspect ratio of 23/10
At the lowest resolution, the image has a size of 320×390 pixels, resulting in an aspect ratio of 32/39, or approximately 11/13
Aspect ratio: variable
Width: scales with browser width, no limit
Height: