Arrow Speed Calculator

IBO Speed Rating is the calculator's unpenalized starting value -- every other input only subtracts a fraction of it through a penalty term. A given percentage change in the rating moves Estimated Speed by roughly the same percentage, while Draw Length, Arrow Weight, and String Accessories each move it by only the specific per-inch or per-grain deduction described above, so the rating dominates the result.

IBO speed is measured at exactly a 30" draw length, and a shorter draw stores less energy in the limbs before release. This calculator applies a standard field-estimate of about 10 fps lost per inch under 30", so a 27" draw on a bow rated at IBO 330 fps would show roughly 30 fps less than the rating before any other penalty is applied.

Within this calculator, yes -- Arrow Weight only ever reduces Estimated Speed once it exceeds the 350-grain IBO test weight, at a rate of about 1 fps per 5 grains over that mark. In the real world a heavier arrow trades some speed for more kinetic energy and momentum downrange, which is often the better trade for hunting; this calculator only reports the speed side of that trade-off.

A peep sight, D-loop, and string silencers add mass directly to the string and cams, which slows the string's return during the shot the same way added arrow weight does, just at a smaller rate -- roughly 1 fps per 3 grains here. It's a small effect individually, but a fully accessorized string can add up to a few fps that a bare IBO number won't show.

It only adjusts for draw length, arrow weight, and string mass relative to the IBO test condition -- it does not model let-off percentage, cam timing or efficiency, arrow spine and stiffness, temperature, or the specific bow's actual power stroke, all of which cause two bows with an identical IBO rating to shoot at different real speeds. Treat the result as a planning estimate and verify with a chronograph.