Recently an artist friend and I were discussing an aspect of painting not often covered in art schools or classes, but perhaps one of the FIRST decisions an artist has to make in setting to work. How BIG...or conversely, how small? The tendency is amongst beginning painters is to choose a canvas of about 16"x20" and make the subject, composition, and technique fit this modest, unintimidating size. From an artistic and learning point of view, there are both good and bad reasons for doing this. It's convenient, but in most cases, tedious. It's inexpensive to do and frame, and easy to place in most homes, but it also dictates to a disturbing degree a tremendous number of limitations as to HOW that beginning painter is forced to work and the amount of painting experience he or she is likely to gain from the effort. But, having said that, a small painting will tend to merely "whisper" any difficulties the artist might have had with some aspect. The same work painted large, can literally SCREAM ineptitude.
From one who's worked both, large and small, the difference has little to do with subject matter. Of course, a tiny kitten, painted five times life size would become a WILD cat, but by and large, the differnce is, I think, the IMPACT the painting has. A very ordinary little still life, when doubled or tripled in size really BLASTS the viewer. It is somewhat the same as music. Low volume music, even hard rock, is easily ignored. The same with a tiny painting. When you pump up the amps, it takes over an INHABITS you. The same with a large painting. I think the determinant as to size (all else being equal), has to do with where that painting belongs, in a home or a showplace. Just as music at a low to moderate level is very comfortable in a home; at a concert, it would be distressing if it were as soft. By the same token, small paintings, no matter HOW exquisite, often get LOST at juried exhibitions.
Quite apart from the above considerations, a large painting allows more freedom of movement and expression as to brushwork, more subtle color expression, and greater room in which to express detail (if you so desire). The tiny painting has more the quality of a jewel, delicate and elegant. Such a painting should hang at eye level in a hallway perhaps, or sit on its own easel on an end table, while the large painting is over-the-couch material. Small paintings are often grouped, especially if there are others of similar subject matter, so that they speak in unison (or sing in chorus so to speak). So, there are no rules, only considerations. I should point out though, either extreme, well done, and displayed in the right context, often garners more attention because of its size than say the run-of-the-mill, average-size canvas. For better or worse, extremes are exciting in art, and they demand respect.