For large screens (desktops), here are the recommended max pixel widths for images to fill their column:
For mobile screens, columns stack so that everything becomes one column. Here is how the different image sizes display on small screens:
Images that are less than 410 pixels wide (height does not matter) do not fill their container on many mobile screens because columns have a max width of 410 pixels on smaller screens. For layouts with three or four columns, use images at least 410 pixels wide to display for all screen sizes and fill their columns.