The two numbers people confuse
Draw length and arrow length are not the same measurement and they are not taken from the same places. Draw length under the AMO convention is measured from the bottom of the nock groove at full draw to a point 1.75 inches forward of the pivot point of the grip. Arrow length, when a shaft is sold or cut, is normally the carbon-to-carbon length: the back of the point insert to the bottom of the nock groove, with the point and the nock excluded. So an arrow cut to exactly your AMO draw length is already projecting roughly 1.75 inches past the deepest part of the grip, which on most bows puts the end of the shaft near or just past the rest before you have added any clearance at all.
That is why this page asks for the clearance separately instead of building it into a formula. Rests sit at different distances forward of the pivot, riser geometry differs, and the amount of shaft you want ahead of the rest is a decision made at the bow with someone watching you draw. What the calculator does is the arithmetic and the bookkeeping, so that the decision you make is the one that gets cut.
Arm span, and why it is only a starting point
Arm span divided by 2.5 is the estimate everyone starts with. Stand with your back to a wall, arms out level, and have somebody else read the tape from fingertip to fingertip — measuring your own arm span produces a number that is always slightly wrong in the direction you were leaning. A 70 inch span gives 28 inches.
It is a population average dressed up as a personal measurement. It knows nothing about your anchor, your head position, how far you rotate your bow shoulder, or whether you shoot with a release aid or off your fingers, and each of those moves the real figure by a quarter inch or more. People with long arms and a short neck come out short; people who anchor deep come out long. Treat the estimate as the number you use to decide that the measured number is plausible, not as a substitute for it.
Why the cut is the irreversible step
Almost everything else in an arrow build can be undone. Points come out, nocks pull off, vanes strip and get replaced, wraps peel. Length does not come back. Once a shaft is short it is short at that draw length forever, and the options are to shoot it at a shorter draw, hand it to someone smaller, or write it off.
There is a second cost that is easy to miss: length and spine are linked. A shorter arrow behaves stiffer, so trimming past what you meant to can push a shaft out of the band it belonged in, and the fix for that is a different shaft rather than a different cut. The sequence that avoids the whole problem is to fix the draw length first, decide the point weight second, check the result against the arrow spine band, and cut third. Cut one shaft deliberately long, check it on the bow, then take the last fraction off it.
The safety part, stated plainly
An arrow that is too short for the draw can be pulled off the front of the rest at full draw. What happens next is not a lost shot; it is a shaft that is unsupported and loaded, and it can break where your bow hand is. The same is true of a shaft that is badly under-spined for the setup, and of any shaft that has already been damaged.
So: a shaft with a crack, a splinter, a dent, a soft spot, or one that sounds dull rather than sharp when you flex and listen to it, is retired. It does not get taped, sleeved, glued or shortened past the damage. There is no repair worth the risk and this page is not going to describe one. Draw length itself, and any change in draw weight or bow setup that follows from it, belongs with a coach and a pro shop who can watch you shoot.
What the length changes downstream
Once the cut length is settled, three other numbers follow from it and are worth working out before you commit. The shaft contributes its grains per inch to the total arrow weight, so an extra inch is real mass. It shifts the balance point rearward, which lowers the front-of-centre figure. And it weakens the dynamic spine. All three show up on the arrow weight and FOC calculator, and the mass figure feeds straight into the kinetic energy and momentum arithmetic. If the length is still genuinely undecided, run those two pages at both candidate lengths and see which of the differences you actually care about.
Questions people ask
How do I work out my draw length at home?
The arm span method gets you close: measure fingertip to fingertip with your arms out level and someone else reading the tape, then divide by 2.5. A 70 inch span suggests 28 inches. What it will not do is account for your anchor, your head position or how much you rotate into the shot, and those are worth a quarter to a half inch each. The reliable version is measured at full draw on a bow with a draw length arrow or a draw board, which is a five minute job at a pro shop and the single measurement most worth having done properly, because everything else on the arrow is derived from it.
How much longer than my draw length should an arrow be?
That is a decision made at the bow rather than a constant. The question being answered is how far ahead of the rest the back of the point should sit at full draw, and the answer depends on the rest, the riser geometry and how consistent your draw is. Around an inch is a common starting point and it is what this page defaults to, but it is entered as an input rather than baked in, because it is not universal. Set it with a coach who can watch you at full draw, then cut the first shaft long enough that you can take another quarter inch off after you have seen it on the bow.
Should I cut arrows shorter to make them stiffer?
Shortening does stiffen an arrow in flight, and it is a real tuning lever, but it is the one lever you cannot reverse. Point weight moves dynamic spine in the same direction and costs nothing to try, so it is normally the thing you exhaust first: reducing point weight stiffens the arrow, increasing it weakens it, and points swap in a minute. If you are still out of range after that, you are probably on the wrong shaft rather than the wrong length. Work out where the setup lands on the spine band before you reach for the saw.
Can I shoot arrows that are longer than I need?
Longer than needed is the safe direction to be wrong, and plenty of people shoot arrows with more clearance than the minimum without any trouble. The costs are real but they are performance costs rather than safety ones: extra shaft is extra grains, the balance point moves back so front-of-centre drops, and the arrow behaves weaker in spine, which may put it outside the band for your draw weight. Too short is the direction that matters, because a shaft that comes off the front of the rest at full draw can break under load.
Does the point count in the arrow length?
Not for the cut, and usually not for the spine chart either. The convention for both is carbon to carbon, meaning the back of the point insert to the bottom of the nock groove, with the point and nock excluded. Overall length including the point is a different figure and is mainly useful for whether the arrow fits a quiver or a tube, and for knowing how far the assembled arrow projects past the rest. This calculator shows both, so there is no ambiguity about which number you are handing to a cutting jig and which one you are comparing against a chart.