WP:IMAGESIZE

Displayed image size
Images adjacent to text should generally carry a caption and use the " " (thumbnail) option, which displays the image at a width determined as follows:
 * A1. For a user not logged in, the width—‌before any scaling due to  (see B below)—‌is currently defaulted to 220px (pixels).
 * A2. For a logged-in user, the width—‌before any scaling due to —‌is as set in that user's user preferences (and this setting is 220px, unless the user has changed it).
 * B. If the  parameter is present, then the initial width determined by A1 or A2 is multiplied by the upright scaling factor.  This allows article editors to adjust the user's "base" image-size preference, according to the characteristics of a particular image. For example:
 * might be used for an image with fine detail, so that it will be rendered "40% larger than the user generally specified".
 * might be used for an image with little detail, which can be adequately displayed "25% smaller than the user generally specified".
 * "Landscape" images (short and wide) often call for  greater than 1. Similarly, "portrait" images (tall and narrow) may look best with   less than1.

Notes:
 * (with  completely missing) multiplies the width by 1.0 (i.e. does nothing)
 * (with  present, but no multiplier given) multiplies the width by 0.75 by default
 * The lead image (appearing at the top of the page) should usually be no wider than  (which is the default equivalent of 300px at preference selection of "220px").
 * scaling factor is not only for thumbnails. It may be used for certain non-thumbnail images that serve much the same function as thumbnails but do not need frames around them or captions below them. In these cases it is necessary to add frameless.

See the for further guidance on expanded or reduced image sizes. Except with very good reason, do not use  (e.g.  ), which forces a fixed image width. In most cases  should be used, thereby respecting the user's base preference (which may have been selected for that user's particular devices). When  is used, the resulting image should usually be no more than 500 pixels tall and no more than 400 pixels wide, for comfortable display on the smallest devices "in common use" (though this may still cause viewing difficulties on some unusual displays). To convert a  value to , divide it by 220 and round the result as desired. For example, 150px is roughly equivalent to 0.7 (150 / 220 = 0.6818...).

Images used in infoboxes are generated by many different means. The most common method used to implement  is Module:InfoboxImage (see documentation there). Alternatively, infoboxes can use standard image syntax in the form of