Arrow spine is the most important specification on an arrow shaft and the one most often ignored by new archers who buy whatever the pro shop has in stock. Wrong spine produces arrows that fishtail, group inconsistently, and lose 30 percent of their potential accuracy regardless of how well the bow is tuned. The shaft is the most personal piece of an archery setup because it has to flex exactly the right amount around the riser on release, and the right amount depends on your specific bow, draw length, and point weight.
This guide explains what spine measures, how to read a manufacturer chart, why dynamic spine matters more than static spine, and how to match arrows to compound and recurve setups with a worked example.
What spine actually is
Arrow spine is a measure of static stiffness. The standard test (ASTM F2031) suspends a 28 inch arrow between two supports 26 inches apart and hangs a 1.94 pound weight from the center of the shaft. The deflection at the center, measured in thousandths of an inch, is the spine. A 400 spine arrow deflects 0.400 inches. A 340 spine arrow deflects 0.340 inches and is therefore stiffer.
Lower numbers are stiffer. Higher numbers are weaker. This catches everyone off guard the first time because it feels backwards: a 500 spine arrow is weaker than a 300 spine, not stronger.
Static spine is just the starting point. Dynamic spine (how the arrow actually behaves when shot from your specific bow) depends on shaft length, point weight, nock and insert weight, fletching, and the bow’s draw weight and energy release profile. A 400 spine arrow cut to 27 inches with a 75 grain point behaves much stiffer than the same shaft cut to 31 inches with a 125 grain point.
Why mismatched spine flies poorly
When the arrow leaves the bow, the string accelerates the rear of the shaft forward before the front catches up. The shaft compresses, flexes, and oscillates around the riser. This is called archer’s paradox, and it is why a tuned arrow can clear a non-center-cut bow at all.
A correctly spined arrow flexes the right amount to wrap around the riser cleanly and recover its straight line within the first 6 to 10 yards. A weak (under-spined) arrow flexes too much, snaps left of straight for a right-handed shooter, and groups left and low. A stiff (over-spined) arrow does not flex enough, kicks right, and groups right and high.
For a compound shooter, the cams release energy so violently that spine tolerance is tighter than for a recurve. A spine that is one column off on the chart usually still groups respectably at 20 yards but opens up to twice the group size at 40. Two columns off and the arrow fishtails visibly in flight. For a recurve, spine tolerance is wider because the energy release is gentler, but spine mismatch shows up as nock left or nock right on bareshaft testing.
How to read a manufacturer chart
Every shaft maker (Easton, Gold Tip, Black Eagle, Carbon Express) publishes a spine chart. The two inputs are draw weight at your actual draw length and finished arrow length. The output is a recommended spine column.
Find your row by intersecting these two values. Easton’s chart, for example, breaks rows into 5 pound bands (60-64, 65-69) and columns into 1 inch bands (27, 28, 29). The chart accounts for cam aggressiveness on compounds with a separate column for hard-cam bows. Soft cams (older or less aggressive) use one column and hard cams (modern hunting cams) shift one column stiffer.
Point weight is the second variable. Most charts are calibrated for 100 grain points. If you shoot 125 grain field tips and matching broadheads, shift one column stiffer. If you shoot 75 grain points (rare in hunting, common in target), shift one column weaker.
Worked example: compound hunting setup
A 28 inch draw length, 65 pound draw weight, hard cam compound shooting a 30 inch finished arrow with a 100 grain field point and 125 grain broadhead.
Start with the chart row for 65 pounds at 30 inches. The base recommendation might be a 340 spine. Shift one column stiffer for the hard cam (no shift on Easton’s modern charts because they already account for it). Shift one column stiffer for the 125 grain broadhead. Final recommendation: 300 spine.
A 300 spine arrow at 8.5 grains per inch finishes around 410 grains with a 125 grain point, fletchings, and nock. That arrow flies flat enough for 40 yard hunting shots and carries enough kinetic energy (around 78 foot-pounds at 290 fps) to pass through a whitetail at any reasonable angle.
Worked example: barebow recurve target
A 27 inch draw length, 32 pound recurve shooting a 28 inch finished arrow with an 80 grain target point.
Recurve charts run weaker because the energy release is slower. The base recommendation at 32 pounds and 28 inches might be a 600 spine. No shift for cam type because there is no cam. No shift for point weight because 80 grain is close to the chart baseline for target arrows.
A 600 spine carbon shaft at 6.5 grains per inch finishes around 270 grains with an 80 grain point. That arrow gives a flat enough trajectory for 18 meter indoor or 50 meter outdoor target shooting.
How to verify your spine choice
Buy two or three shafts of your chart-recommended spine before committing to a dozen. Shoot bareshafts (no fletching) at 15 yards alongside fletched arrows. The bareshafts should group within 4 inches of the fletched group. Bareshafts grouping left of fletched for a right-handed shooter mean the arrows are weak. Bareshafts grouping right mean stiff. Bareshafts grouping with the fletched arrows mean the spine is tuned.
Walk-back tuning at 5, 10, 20, and 30 yards confirms the choice further. The arrows should print on a vertical line; drift left or right at distance indicates spine error not corrected by rest position.
When to ignore the chart
Compound finger-shooters need stiffer arrows than the chart suggests because finger release adds horizontal force the chart does not model. Bowfishing arrows ignore spine entirely because the heavy fiberglass shaft and short distance mask the effect. Indoor 40 cm target shooters often choose two or three columns stiffer than the chart for the larger shaft diameter that catches more line breaks.
For any other use, the chart is a starting point that gets you within one column of correct, and bareshaft tuning gets you the rest of the way.
Frequently asked questions
What does arrow spine actually measure?+
Spine measures the static stiffness of an arrow shaft. A 28 inch arrow is suspended between two supports 26 inches apart, and a 1.94 pound weight is hung from the center. The deflection in thousandths of an inch is the spine. A 400 spine arrow deflects 0.400 inches under that load. Lower numbers mean stiffer arrows. Dynamic spine (how the arrow actually flexes when shot) depends on length, point weight, and bow energy on top of that static number.
What happens if my arrow spine is too weak or too stiff?+
Weak (under-spined) arrows flex too much on release, fly tail-left for a right-handed shooter, and tend to group low and left. Stiff (over-spined) arrows flex too little, fly tail-right, and group high and right. With a compound, a spine that is one column off in either direction usually still groups acceptably but loses 10 to 15 percent of group consistency. Two columns off and accuracy collapses.
Does cutting an arrow shorter change its spine?+
Yes. Cutting an arrow stiffens it dynamically. A 400 spine arrow cut from 30 inches to 28 inches behaves roughly like a 380 spine arrow. Most chart calculators ask for finished arrow length precisely because the dynamic spine depends on it. If you draw 28 inches but cut the arrow at 29 to leave clearance past the rest, use the finished length (29) in the chart.
How much does point weight matter?+
A lot. Every 25 grain change in point weight shifts dynamic spine roughly one column on most charts. Switching from a 100 grain field point to a 125 grain broadhead weakens the dynamic spine. If you are right on the edge of a spine column, that change alone can move your group several inches. Always tune with the point weight you will actually shoot.
Do I need different spines for indoor and outdoor target shooting?+
Often yes. Indoor archers commonly use much stiffer, heavier shafts (250 to 350 spine, 25 to 30 grains per inch) for the large diameter that catches line breaks on 40 cm faces. Outdoor target archers use lighter, weaker spines (400 to 600) for flatter trajectories at 70 meters. Hunting arrows split the difference at 300 to 400 spine and 8 to 12 grains per inch.
