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Free bow hunting arrow spine calculator for a starting carbon-style spine class. Enter peak draw weight, arrow length, hunting point weight in grains, and bow type to see a spine grouping and stiffer or weaker alternates—then confirm with your shaft maker's chart and paper tuning.
Last updated: April 17, 2026
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Carbon shaft cut length / AMO-style shaft measure you use for charts.
Field tip or finished hunting point plus insert as you shoot it.
Starting spine class
400
Weaker = higher #
Demand score
179.5
If flight is stiff or weak, try:
340 (stiffer) · 500 (weaker)
Spine numbers are industry-style groupings (weaker = higher number). Broadheads, nock end weight, draw length vs rated weight, and cam aggression all change dynamic spine—paper-tune and follow your shaft maker’s chart.
Safety & ethics:
Inputs
30–85 lb · 50–200 gr
Lever arm
Longer = more demand
Offset
Simple energy model
Carbon-style labels
Common retail bins
Direction
Paper & bare shaft
Heuristic
Compare scenarios
60 lb recurve, 29 in arrow, 100 gr point (defaults):
Spine ~ 400
Demand score 179.5 · try 340 (stiffer) · 500 (weaker)
Static spine tables from manufacturers fold together draw weight, shaft length, point weight, and sometimes bow speed or IBO rating. This calculator uses a compact weighted sum—draw weight scaled by 2.8, length relative to a 27-inch reference, point weight relative to 90 grains, and a small bow-type offset—to place you in a common carbon spine bin. Higher demand maps to a stiffer shaft class (smaller spine number). It cannot model every cam system, nock weight, or vane drag combination.
demand = 2.8×draw(lb) + 5×(length−27 in) + 0.15×(tip−90 gr) + bow offsetBow offset is +10 for compound, −5 for traditional, 0 for recurve. Demand bands map to spine classes from 250 (stiffest here) through 800 (weakest).
Also see our FPE calculator for arrow kinetic energy checks alongside spine tuning.
Get Custom Calculator for Your PlatformShare it with bow hunters building a first arrow list or tuning broadheads.
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