I use a program like The Archery Program or OnTarget, there is another one but I keep forgeting the name. They are a bit more accurate than using a simple chart or online calculator since you can enter more data. Most of the charts or online calculators either ask for draw length or arrow length assuming you use the correct length arrows for your set up. The programs you can enter both along with other factors to narrow your choices down a little bit more.

None of them are exact though and you still need to check your set up to see if it shoots well and may need to play with it a bit to get it perfect.

Excellent post Arthur!