Archery Blog
Arrow Spine Chart Explained: How to Read the Numbers and Pick the Right Stiffness
May
The first time you look at an arrow spine chart, the numbers feel backwards. A 340 spine is stiffer than a 500. A heavier point makes your arrow act weaker, even though you didn’t change the shaft. And two archers shooting the same bow can end up on completely different rows of the chart. Spine isn’t a single property of the arrow — it’s the relationship between the shaft’s stiffness and everything your bow does to it during the shot. Once you understand what each column on the chart is actually asking, picking the right arrow stops feeling like a coin flip.
What Spine Actually Measures
Spine is a measurement of how much an arrow shaft flexes when force is applied to it. The ATA (Archery Trade Association) standard suspends a 28-inch shaft between two supports 28 inches apart, hangs a 1.94-pound weight from the center, and measures the deflection in thousandths of an inch. An arrow that bends 0.400 inches under that load is called a 400 spine. One that only bends 0.340 inches is a 340 spine — and because it bends less, it’s stiffer.
That inverted scale is the first thing that trips people up. Lower number equals stiffer arrow. Higher number equals weaker arrow. Once you internalize that, the rest of the chart starts making sense, because every variable that increases the force on your shaft pushes you toward a lower (stiffer) spine number.
Static vs Dynamic Spine
The number printed on the shaft is the static spine — measured at the factory on a test fixture. What actually matters when you shoot is the dynamic spine, which is how the arrow flexes during the violent acceleration of release. Dynamic spine depends on draw weight, draw length, point weight, arrow length, nock and insert weight, even the cam aggressiveness of your bow. The spine chart is a lookup table that translates your shooting setup into the static spine number that produces the right dynamic behavior.
Reading the Chart Column by Column
Every manufacturer’s chart — Easton, Gold Tip, Victory, Black Eagle — uses the same basic structure, even though the styling differs. Down the left side you’ll find draw weight. Across the top you’ll find arrow length. The cell where your row meets your column gives a recommended spine, usually for a standard 100-grain point. Get any of those three inputs wrong and the chart hands you the wrong arrow.
Draw Weight
This is the peak holding weight of your bow, not the let-off weight a compound holds at full draw. A bow set at 60 pounds delivers 60 pounds of force into the arrow at the start of the power stroke, even though you’re only holding 12 pounds at the back wall. Heavier draw weight means more force, more flex, and you need a stiffer arrow. If your chart row jumps between weight brackets (say 60–65 and 66–70), and you’re at 65 exactly, pick the stiffer bracket — it’s safer to be slightly over-spined than under.
Arrow Length
This is the length from the throat of the nock to the end of the shaft — not the overall arrow length including the point. Longer shafts flex more because there’s more unsupported material between the nock and the point, so longer arrows need stiffer spines. The difference between a 28-inch and a 30-inch shaft can move you a full spine size. Measure from your nock throat to where the back of your insert seats, not from the nock to the tip of the broadhead.
Point Weight
Most charts assume a 100-grain field point. If you shoot 125-grain heads, or stack a 50-grain insert behind a 100-grain broadhead, your effective point weight is higher and your dynamic spine becomes weaker — the heavier mass at the tip drags during acceleration, exaggerating shaft flex. Manufacturers handle this with a footnote: “For every 25 grains over 100, move one row stiffer.” A 60-pound bow at 29 inches with 150-grain points doesn’t pick the same arrow as the same setup with 100-grain points.
The Hidden Variables Charts Don’t Always Show
The three columns above get you 80% of the way to the right arrow. The other 20% lives in fine print most archers skim past, and those details are why two people with identical setups sometimes end up on different shafts.
Cam Aggressiveness
A hard cam — one that dumps energy aggressively at the front of the power stroke — loads the arrow harder than a smooth cam at the same draw weight. Modern speed bows with sharp force-draw curves often require one spine size stiffer than the chart recommends. Easton publishes a “hard cam” footnote on most of their charts for this reason. If your bow advertises IBO speeds above 340 fps, assume you fall into that category.
Insert and Nock Weight
Aluminum inserts run 15–20 grains. Stainless or brass HIT inserts push 50–75 grains. Heavy inserts behave like extra point weight — they shift mass forward and weaken dynamic spine. Same with nocks: a lighted nock at 25 grains versus a standard 10-grain nock changes the rear balance enough to nudge tuning, especially at short distances.
Release Style
Finger shooters and traditional archers need significantly weaker arrows than compound shooters using mechanical releases. Fingers introduce sideways flex (archer’s paradox) at release; the arrow must bend around the riser. A mechanical release lets the string travel straight, so the arrow flexes vertically rather than horizontally and tolerates much stiffer shafts. Recurve and longbow charts are entirely different documents — never use a compound spine chart for a finger release setup.
Common Spine Numbers and Where They Land
For carbon arrows on modern compound bows, four spine numbers cover the vast majority of setups:
- 500 spine — Light setups, typically 40–55 pound draws with shorter arrows. Youth bows, light hunting rigs, and many women’s compound setups.
- 400 spine — The most popular hunting spine. Fits roughly 55–65 pound bows at 28–29 inch arrows with 100-grain points.
- 340 spine — Heavy hunting and target setups. 65–75 pound draws, or 60-pound bows with long arrows or heavy broadheads.
- 300 spine — High-draw-weight hunting, long arrows, or shooters running 125+ grain heads on aggressive cams.
- 250 spine — Specialty: very high draw weights (75+ pounds), heavy single-bevel broadheads, or long-bowstring traditional setups with high poundage.
Target archers often run stiffer-than-needed arrows because they prioritize tight groups at long distance — a slightly over-spined arrow recovers faster from launch and clears the rest more consistently. Hunters tend to run closer to the chart’s nominal recommendation because heavier arrows penetrate better, and dropping spine usually means dropping shaft weight.
Bare Shaft Tuning: The Chart’s Final Check
A spine chart is a starting point, not a final answer. The honest test is bare shaft tuning — shooting an unfletched arrow alongside a fletched one at 15–20 yards and watching where it hits relative to the fletched group. For a right-handed compound shooter:
- Bare shaft hits left of the fletched group → arrow is too stiff. Add point weight, lengthen the shaft, or step weaker (higher number).
- Bare shaft hits right of the fletched group → arrow is too weak. Reduce point weight, shorten the shaft, or step stiffer (lower number).
- Bare shaft high → nock point too low.
- Bare shaft low → nock point too high.
Mirror the left/right results for a left-handed shooter. Bare shaft tuning will tell you in five minutes whether the chart picked the right arrow for your specific bow, form, and release — and it catches edge cases the chart can’t predict, like a torquing grip or a slightly off cam timing.
Why Two Charts Disagree About the Same Setup
Run your numbers through Easton’s chart, then through Gold Tip’s, and you’ll occasionally get different recommendations. This isn’t a sign that one company is wrong. Each manufacturer builds their chart around the construction of their own shafts — the wall thickness, the carbon weave, the inner liner. A 340 spine from one brand is built to the same ATA standard as another brand’s 340, but the way it behaves dynamically in the seconds after release depends on the shaft’s mass distribution and stiffness profile along its length.
Use the chart from the manufacturer of the arrow you’re actually buying. If you switch brands, re-check — your tuning may shift even though the spine number on the label is the same.
When the Chart Falls Short
Three situations the standard spine chart handles poorly:
Extreme FOC Builds
Front-of-center percentages above 20% are popular among bowhunters chasing penetration on tough game. Running a 250-grain broadhead with a 100-grain insert on a 60-pound bow puts roughly 350 grains at the tip — far outside what most charts model. You’ll need to step at least two spine sizes stiffer than the nominal recommendation, then bare shaft tune from there.
Crossbow Bolts
Crossbow bolts use their own spine system that doesn’t translate to vertical bow charts. Crossbow energy delivery, rail contact, and shaft length conventions are different enough that vertical bow charts will mislead you. Always use crossbow-specific charts when shopping bolts.
Recurve and Longbow Setups
Traditional bows demand weaker spines than the same draw weight on a compound, often dramatically so. A 50-pound recurve at 28 inches typically takes a 500 or even 600 spine carbon arrow — territory that would be far too weak for any compound at the same weight. Wood arrow spine is measured in pounds (e.g., “45–50 pound spine”) rather than thousandths, and the math doesn’t cross over. Use a recurve-specific carbon chart, or a wood arrow chart, depending on your shaft material.
A Worked Example From Chart to Arrow
Take a compound shooter at 65 pounds peak draw, 29-inch draw length, planning to shoot a 28-inch arrow (measured nock throat to insert seat) with a 100-grain field point. Open Easton’s chart. Find the 60–70 pound row. Move across to the 28-inch column. The cell points to a 340 spine in the Axis line. The shooter buys 340s, cuts them to 28 inches, and shoots bare shaft alongside fletched. Bare shafts impact slightly left of the fletched group at 15 yards — meaning the arrow is showing as marginally stiff, which is exactly where most archers want to land. They could leave it alone, add 25 grains to the point to weaken it slightly, or move on to broadhead tuning. The chart got them to within one tuning adjustment of perfect.
Now swap one variable: same archer, same bow, but 125-grain broadheads. The point-weight footnote applies. Either step one row stiffer on the chart, or stay at 340 and expect to bare shaft tune toward a weaker setup by shortening the shaft slightly. Same archer, different broadhead, potentially different arrow row.
The Mental Model That Sticks
Anything that adds force during the shot — heavier bow, longer arrow, heavier point, more aggressive cam — pushes you toward a stiffer shaft (lower number). Anything that reduces force — lighter bow, shorter arrow, lighter point, smoother cam — pushes you toward a weaker shaft (higher number). The spine chart is just a structured way to add those factors up and read off the matching shaft, with bare shaft tuning as the final correction for everything the chart can’t see. Once that mental model clicks, you stop guessing and start fixing.
Sources
- Easton Archery — Shaft selector and spine chart documentation
- Gold Tip Arrows — Hunting and target arrow spine charts
- Victory Archery — Carbon arrow technical specifications
- Archery Trade Association — ATA spine measurement standard
- Wikipedia: Arrow — General reference on arrow construction and dynamics
