Arrow Spine Calculator
Spine is the shaft's stiffness, and it has to match your bow. Enter draw weight, arrow length and point weight for your spine group — then read it against the full selection chart below.
Spine Selection Chart
Static spine group by draw weight (columns) and finished arrow length (rows), in the common Easton-style groupings for carbon hunting shafts with standard inserts. Smaller number = stiffer shaft.
| Length | Under 35 lb | 35–45 lb | 45–55 lb | 55–65 lb | 65–75 lb | 75 lb + |
|---|---|---|---|---|---|---|
| 26″ | 600 | 500 | 400 | 400 | 340 | 300 |
| 27″ | 600 | 500 | 400 | 340 | 340 | 300 |
| 28″ | 500 | 400 | 400 | 340 | 300 | 300 |
| 29″ | 500 | 400 | 340 | 340 | 300 | 300 |
| 30″ | 500 | 400 | 340 | 300 | 300 | 300 |
| 31″ | 400 | 340 | 300 | 300 | 300 | 300 |
Building the arrow first helps: total weight and point weight come from the arrow weight calculator, and the balance check lives on the FOC calculator. Spine, weight and FOC are one decision made in three places.
Adjustments to the Chart Answer
Point weight: the chart assumes a standard 100–125 gr point. At 150 gr and above, treat the arrow as one group weaker — pick the next number up, or confirm with a bare-shaft tune.
Aggressive cams: hard-cam compounds drive the shaft harder than the draw weight alone suggests; bows at the top of a band often shoot better one group stiffer.
Length: the chart reads your finished length, nock throat to insert face. Two inches of length is worth roughly one spine group.
However you arrive at the group, confirm against your shaft maker's own chart before buying a dozen — makers' labels differ by small amounts that matter at the extremes.
Spine Worked Examples
65 lb and a 28.5″ arrow lands in the 65–75 lb column at the 29″ row: 300 spine — the group most modern hunting shafts are sold in.
A 40 lb bow with a 27″ arrow reads the 35–45 lb column: 500 spine. Light bows forgive more, but the group still matters for clean flight.
70 lb, 30″ arrow: the chart says 300. Add a 200 gr point for an FOC build and the dynamic behaviour drops a group — most archers buy the 300 and tune, or step to the stiffest shafts their maker offers.
Spine FAQs
What does the spine number actually mean?
Spine is stiffness, measured as deflection: the shaft is supported at two points 28 inches apart, a 1.94 lb weight is hung in the middle, and the bend is read in thousandths of an inch. A "340 spine" shaft deflects 0.340 inches. Smaller number, stiffer arrow — the opposite of what most people guess first.
What happens if my spine is too weak or too stiff?
Too weak (number too high for your setup) and the arrow flexes excessively — erratic broadhead flight, torn paper-tune holes that won’t correct, and in extreme cases a shaft that fails at the shot. Too stiff and the arrow won’t flex around the riser cleanly, giving stubborn left-right tears and poor broadhead grouping. Both are tuning problems before they are accuracy problems.
Does cutting my arrows shorter change the spine I need?
Yes — length is half the selection chart. A shorter arrow behaves stiffer, a longer one weaker, roughly one spine group per two inches. If you cut a shaft down after buying it, re-check the group here; the same shaft at 27 inches and 30 inches is effectively two different arrows.
How does point weight affect spine?
A heavier point makes the arrow behave weaker — the front end resists the push longer. Going from 100 to 150+ grains up front commonly moves a setup one group weaker (the next number up), which is why high-FOC builds often need a stiffer shaft than the chart’s first answer.
Is this chart the same for carbon and aluminum arrows?
The grouping logic is the same — spine is spine, whatever the material — but always confirm against your shaft maker’s own chart before buying, because makers measure and label with small differences. This chart follows the common Easton-style groupings for standard hunting setups.
- Easton Archery — shaft selection charts — the reference spine-selection and arrow-building charts this site’s groupings follow
- Gold Tip — arrow university and spine charts — manufacturer spine charts and arrow-weight data used to cross-check the tables