Википедиа:WikiProject Geographical coordinates/dim:

The dim: parameter specifies the width of the object in metres or kilometres, overriding the scale implied by any type: parameter.

Syntax — dim:<width><units>

width — integer number of metres (m) or kilometres (km)

units — m or km, if not specified, defaults to m

GeoHack uses dim: to select a map scale. If no dim:, type:, or scale: parameters are provided, GeoHack uses its default scale of 1:300,000.

Samples

Subject	Dim	Markup	Result
Buckingham Palace	120m	{{coord|51.501|-0.142|dim:120m}}	51°30′04″ с. ш. 0°08′31″ з. д.
London	10km	{{coord|51.507222|-0.1275|dim:10km}}	51°30′26″ с. ш. 0°07′39″ з. д.