you answered your question in your own post. The maps width and length have to be 'a dimension of 32' this means it has to be a multiple of this value.
so the smallest map size is 32x32 now you can make it bigger by simply making it any other size of this format (32*n)x(32*m) where n and m can be any natural number (1,2,3,4,.....).
n and m do not need to be the same value.
so sizes like 64x64, 96x32, 256x128 are also possible.
The maximum map size is 256x256 (or maybe bigger, here I'm not really sure)