Asically I think that every portrait needs its own space. Depending on the composition, which is determined by the picture to work, I choose the portrait format size. Sometimes the face expression requires more space around or the contrary. The same thing happens with figures. I generally use two standard sizes for pastel portrait, which are determined by the paper I use, Canson paper. The larger size is 16x20 "(40.5x51 cm), which I usually apply for half-length figure with hands. The other one 12x16 "(30x40 cm), is more suitable for head and shoulders (bust). I’ve also started to work lately a lot in “almost carre”, drooping that last size I’ve mentioned before, which gives me 11 x 14” (28x35.5 cm). For Oil Portrait paintings sizes are much more extensive and varied. The portrait study is treated more like a painting, but the most common standard sizes are as follows; 24x20 "(61x51 cm) and 30x24" (76 x 61 cm). If you need a concrete or different size please notify me. I’ll do the same if I think that your picture requires it.