Wikipedia:Extended Image Syntax - Detailed Syntax - Size

Size

Zero or one of these options may be specified to control the size of the image. In the case of images with captions, if the image is already smaller than the requested size, then the image retains its original size (it is not enlarged). In the case of images without captions, the image will be enlarged or reduced to match the requested size. Sizing is disabled when a 'frame' is used.

Widthpx

(E.g., "100px".) Scale the image to make it the specified number of pixels in width, and scale the height to retain the original aspect ratio.

xHeightpx

(E.g., "x150px".) Scale the image to make it the specified number of pixels in height, and scale the width to retain the original aspect ratio.

WidthxHeightpx

(E.g., "100x150px".) Scale the image to be no wider and no higher than the specified number of pixels. The image will keep its original aspect ratio.

(nothing specified)

For thumbnails, use the size specified in preferences for logged in users, and use a size determined by resolution for anonymous users. For non-thumbnails, use the native size of the image.

upright

Scale a thumbnail image to 75% of normal thumbnail width, rounding the result to the nearest multiple of 10 pixels.

upright=Factor

Adjust a thumbnail's size to Factor times the default thumbnail size, rounding the result to the nearest multiple of 10. For instance, "upright=1.5" makes the image larger, which is useful for maps or schematics that need to be larger to be readable. The parameter "upright=1" returns the same size as thumbnail width, and "upright=0.75" is functionally identical to "upright" alone.

The "upright" option must be used along with the "thumb" parameter.