Isn't 48x48 a standard tile size? If you're smaller than that rocking 32x48 you should have no problem following the size of a block.
That means if you do 48 * 3 (because there are 3 sprites: Walk Left, Stand, Walk Right) then you get 144 wide.
If you do 48 * 4 (because there are 4 sprites: Down, Left, Right, Up) then you get 192 tall.
So you can easily rock a 144 x 192 sprite sheet.
If you want to be exact with your character then it's 96 x 192.
If you're only getting half of your character's face, it means that the alignment of your sprites aren't correct. Adjust them accordingly.