The archery arrow spine calculator uses the AMO dynamic spine formula to recommend the correct arrow spine for your bow setup. Dynamic spine accounts for draw weight, draw length deviation from 28", point weight, and arrow length — the four variables that determine how an arrow actually behaves in flight. Note: this tool selects spine; for weight/FOC/KE calculations, see the Arrow Build Calculator.
Standard hunting: 100gr. Field: 75–100gr. Heavy: 125–200gr.
Compatible Arrow Shafts
Note: Archery uses imperial measurements (inches, grains, lbs) as universal international standards. Display values in the system above.
How to Use the Archery Arrow Spine Calculator
Arrow spine selection is the first step in building a tuned arrow setup. An arrow that's too weak (too flexible) will kick to the left for right-handed archers; too stiff and it will kick right. Correct spine produces straight, consistent flight.
The Dynamic Spine Formula
The AMO dynamic spine calculation adjusts your actual draw weight by: adding approximately +2 lbs per inch of draw length over 28" (or -2 lbs per inch under 28"), adding +5 lbs for each 25 grains of point weight over 100 grains, and adding approximately +1.5 lbs per inch of arrow length over standard. This effective draw weight maps to the spine number you need.
Reading the Spine Number
The recommended spine is a static deflection number — .300 (stiffer) through .700 (more flexible). Most hunting arrows come in .300, .340, .400, .500, .600, and .700 spine variants. Carbon Express, Easton, Victory, and other manufacturers publish spine charts that match these numbers to their product lines.
After Selecting Spine
Once you have your spine, use the Arrow Build Calculator on this site to calculate FOC, total arrow weight, kinetic energy, and momentum from your chosen components. Spine selection comes first; build optimization comes second.
FAQ
Is this arrow spine calculator free?
Yes, completely free with no signup required. All calculations run locally in your browser.
What is dynamic spine?
Dynamic spine is the actual bending behavior of an arrow during flight, accounting for draw weight, draw length, arrow length, and point weight. It differs from static spine (a standardized stiffness measurement made with a 1.94 lb weight on a 28-inch arrow) — dynamic spine is what matters for actual arrow flight.
How is this different from the Arrow Build Calculator?
The Arrow Build Calculator (also on this site) calculates total arrow weight, FOC percentage, kinetic energy, and momentum from component weights. This Spine Calculator focuses specifically on which spine rating to SELECT before building — it's the first step in arrow selection, not assembly.
How do draw length and draw weight affect spine selection?
Longer draw length increases effective arrow shaft length and creates more bend — requiring a stiffer (lower number) spine. Higher draw weight also requires stiffer spine. Each inch over 28 draw length typically requires about 5 lbs more effective draw weight in spine calculations.
What does the spine number mean?
Arrow spine is measured in thousandths of an inch of deflection under a 1.94 lb load on a 28-inch span. A .300 spine deflects 0.300 inches (stiffer). A .600 spine deflects 0.600 inches (more flexible). Lower numbers = stiffer arrow. Recurve archers reverse this: lower number spine flex = stiffer.
Should I round up or down spine if between sizes?
If shooting a recurve, err on the stiffer side (lower number). For compound with a mechanical release, err on the weaker side (higher number). The compound release produces less paradox (less lateral kick) than a finger release, so compounds can tolerate weaker spines better.