Archery calculators

Bow setup is a chain of dependent numbers. Your draw length sets your usable arrow length, arrow length and point weight shift dynamic spine, spine choice constrains total arrow weight, and total weight decides both speed and kinetic energy. Change one and the rest move with it. These calculators exist so you can walk that chain in order instead of guessing at the end of it.

Start with draw length, because almost everything downstream depends on it. The wingspan method, arm span in inches divided by 2.5 and rounded to the nearest half inch, gets most archers within half an inch of correct. From there, arrow spine tells you which shaft stiffness your draw weight, arrow length and point weight actually call for. Spine is dynamic rather than a single printed number: a heavier point or a longer arrow both weaken it, and an aggressive cam stiffens what you need.

Once a shaft is chosen, total arrow weight adds up the components, shaft, insert, point, nock and fletching, into the finished grain weight that everything else keys off. That number carries the one hard safety rule in arrow building: never shoot less than 5 grains of total arrow weight per pound of draw weight. Below that floor you risk damaging the bow and you void most warranties.

Arrow speed translates an IBO rating into the fps your setup will really produce, since IBO is measured at a 30 inch draw, 70 pounds and a 350 grain arrow, which describes almost nobody. Kinetic energy and momentum then tell you what that arrow carries downrange, and FOC tells you how the weight is distributed front to back. Angle compensation is the field tool: shooting up or down always plays shorter than the line of sight distance, because gravity only acts over the horizontal component.

Results here are researched guidance, not a substitute for a bow press and a qualified pro shop. Confirm draw weight, spine and broadhead choices with your bow manufacturer's specifications before you shoot. See also the reference charts and the setup guides.