Hi Chancy,
I usually start with a 1/4 ounce (7g) on most 1/2A planes. Hard to know for sure, but get someone who knows how to watch the wings on your trim flights, right side up and inverted. You probably know that.
Rusty

Chancey, a quarter oz for starters should be fine. A wise ol' control line flyer in a personal message told me when I asked the same question, " Too much tip weight may cost a few pattern points in competition, too little may cost you an airplane"!! Just gotta love 1/2a stuff!!!   

Thanks again.  I would like to make a wingtip weight box, but I am not sure how to make one, let alone one that small.  It is just for fun flying, but i will research a bit.  I will not cover it till springtime here as mama would NOT appreciate the smell in the house.

It's never a certain weight.  It's how much weight it takes to move the CG outboard of the thrust line.  The position of the CG vs the thrust line determines whether the airplane will turn left or right.  Too much line pull is better than none at all.

Gotta put my two cents worth in.   

Two cents is 5.0 gr. (Each penny is 2.5 gr.). That is a good place to start on many 1/2A planes. With a built-up wing you can make a tip weight box. For adjusting tip weight some use small fishing line weights. Those are good because you know how much each weighs.

Some of us old guys have been known to use Ambroid (or other) glue tubes as tip weight. Then there is always a chunk of solder.

How much effort you put into it determines the accuracy of your outcome. If you put in enough effort it will become easier each time you do it until it becomes just another building step.

Good luck whichever way you choose.

Oh, one more thing...tip weight access looks MUCH better on the BOTTOM of a wing. 

George