Archery Arrow Spine Calculator
Adjusted Draw Weight (lbs)
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Recommended Spine (deflection)
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Min Arrow Weight (grains)
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Grains per Pound
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Understanding Arrow Spine
Arrow spine refers to the stiffness of an arrow shaft, measured by how much it deflects (bends) under a standard weight. A lower spine number means a stiffer arrow. Correct spine matching is essential for arrow flight accuracy and safety.
The recommended spine depends on draw weight, draw length, arrow length, and point weight. Higher draw weight requires stiffer arrows (lower spine number). This calculator adjusts for these factors to provide a starting recommendation.
Arrow weight should be at least 5 grains per pound of draw weight for safety. A 50 lb bow needs arrows weighing at least 250 grains. Heavier arrows are quieter and transfer more energy; lighter arrows are faster but noisier. Always consult manufacturer spine charts for your specific bow and arrow combination.
Frequently Asked Questions
What is arrow spine?
Spine is the stiffness rating of an arrow. It's measured by deflection (in thousandths of an inch) when a weight is hung from the center of the shaft.
What happens with wrong spine?
Too weak (high spine number) causes arrows to flex excessively, fishtailing in flight. Too stiff (low spine) causes arrows to fly left (right-handed) and not group well.
How does draw weight affect spine?
Higher draw weight needs stiffer arrows. Every 5 lbs of draw weight roughly shifts you one spine group (e.g., 500 to 400).
What is grains per pound (GPP)?
Total arrow weight divided by draw weight. Minimum 5 GPP for safety. 6-8 GPP is a good hunting range. 10+ GPP is heavy/quiet.