Bryce, I start out with most of mine being 15 - 18 inches, or fore arm length like Bubby said. Depending on how far the dart is going be thrown, I take off length from the thrower. For the ones I use for hunting, with shots hopefully being 10- 15 yards, I go with a 18" thrower and darts that are about 5.5 feet long (including foreshaft). For bow fishing, where my shots are under 5 yards, I use a shorter thrower (14-15 inches) and shorter darts. For fun and long distance throwing, I have a couple that are 20 + inches with darts that are 6 ft +. Just start making them and see what works for you. Good thing about them is you can get as elaborate as you want, or keep it as simple as you want. I seen the President of the Missouri Atlatl Association go cut a fork out of a little sapling, cut the limbs off, leaving it looking like a stick that you would roast wieners with. He wrapped a string between the points and used darts with nocks cut into them like arrows. He kicked butt with that setup!
And you can use scrap pieces of wood from wood building to make them from too. I have a whole box of wood pieces that I am planning on making throwers with. Every time I get nice scrap, it goes in the box for future use (but I am also a wood hoarder...but that is another story : ) ). Good luck with the atlatl making!
Neal
