Your handle is usually 4" long, I make mine as suggested for the most part.
I put a center line on the stave and use a circle template to lay out my bow, this way is very precise.
My handle layout is the same, at the center of the handle I draw a 1 1/4 " circle, at the ends of the 4" handle section I draw a 1" circle for the arrow pass and make the other end the same for symmetry, 2 3/4" out from the ends of the handle I draw a 1 1/4" circle.
This makes a nice handle with a gradual transition from the handle, through the fades and out to the limb. The 2 3/4" fades will shorten a bit when I tiller to get this area bending a little. I connect the dots by drawing a line at the outside edge of the circles with a ruler to give me my cut lines. I cut outside the lines and use a file to remove wood down to my lines.
Your finished handle with my layout will look something like this;
I make my tips 9/16" initially and drop them to between 3/8" and 1/2" about the time I do the final shaping on the finished bow, I start my taper to the tips at 12".