If you have a known starting weight the best way to do it sans-scale is with liquid as sickboy mentioned. Another technique is to powder all of it to a very dusty texture and make equal looking piles on grid paper, but this is much less accurate. You should always use a scale though because unless you weighed it yourself you will not know for certain exactly how much starting material you have, vendors sometimes give extra and with some drugs a few mg extra is too much. With other drugs it is less important though, I never use a scale to measure ketamine because I don't care if I am off by 100 MG.