In order that the dimensions of an object can be read with any accuracy, it's best to make the drawing to a certain scale, which in the case of house or commercial building plans is usually 1/4" = 1'-0". This means that every quarter inch of the drawing is considered to be one foot in actual construction, and every 1/8th of an inch will represent six inches. When referring to the dimensions of a drawing it's usually customary to show only the real or full size dimensions of the object, regardless of the smaller size that it may be necessary to create the drawing on paper. If we don't do this, we may wind up with a bunch of confusion.
The size of the scale is the choice of the drafter, or the size of the paper that the drawing has to be drawn on. In architectural work scales of 1/4" = 1'-0" and 1/8" = 1'-0" are commonly used for the construction plans of buildings, while other scales such as 1/2" = 1'-0". and 3" = 1'-0" are used for parts which require a more complete visible clarity. These drawings are known as details.
Special measuring instruments known as Architects or Engineers scales are made with graduated divisions to indicate the several scales used. These instruments, or scales, are not absolutely necessary, as any scale divided into sixteenths of an inch may be used for a variety of scales by a little mental effort in conceiving one or more of its divisions as representing the desired unit for the reduced scale. It's just easier to use a scale made to read these reduced dimensions.