half eighth (1/8 divided by 2) of marijuana is called a teenth (1/16)
meaning it is 1/16th of an ounce
now lets do the maths!!
1 ounce = 28.349523125 grams (hey i just done you some research.... let's round this up to 28.35g)
28.35g / 16 = 1.77 grams of marijuana
now.. if you have a good dealer or grow your own it will not have any 'additives'. and this may be enough for a couple of spliffs depending what size they are.