Size in tapestries usually means their physical size, which we will talk about. But also, "size" of tapestry wall hangings in a room is often a function of the brightness of color(s), placement and lighting, and whether it is used as background or foreground.

A large tapestry occupying 80% or more of the wall with furniture and other objects in front of it will render the tapestry as background. It will perform the function as a wall mural, which is the traditional way tapestries were used. If, however, the same tapestry occupies all of the wall space without anything in front of it, the tapestry becomes foreground, taking greater prominence in the room.

Similarly, your room size will affect the impact of your tapestry. A tapestry wall hanging normally viewed from 10 feet away will look different viewed regularly from say 30 feet away. Also, overall color "strength" will increase or decrease the effect in a room. For instance, a pastel palette tapestry will be softer and blend, whereas a brightly colored tapestry will be truly "outstanding"! You will find that tapestries are very accommodating. You can use them as "woven pictures" in small spaces or you can treat them like "woven murals" in medium and large spaces. As a general principle, tapestries tend to realize their fullest potential when displayed in larger sizes.
Our advice-choose the design(s) and colors you love first, then consider the size. As architectural detail, a tapestry should be scaled to the room and the wall-neither too large nor too small. A rule of thumb: it should occupy 80% (or more) of the intended space.