Arrow Spine Calculator
Find the correct arrow spine stiffness for your bow draw weight, draw length, and arrow length.
Avoid poor arrow flight and inconsistent accuracy.
Arrow spine is the stiffness rating of an arrow shaft. It is one of the most critical factors in archery accuracy. An arrow that is too stiff (over-spined) or too flexible (under-spined) will not fly straight and will produce inconsistent groups.
Arrow spine is rated numerically — lower numbers mean stiffer arrows. Common ratings: 250 (very stiff, for high poundage bows), 340, 400, 500, 600 (flexible, for low poundage bows).
The static spine test deflects an arrow at its center under a 1.94 lb (880g) load. The deflection in inches, multiplied by 1000, gives the spine rating. A 0.400-inch deflection = 400 spine.
Key factors affecting spine selection:
- Draw weight — The primary driver. A 60 lb recurve needs stiffer arrows than a 35 lb beginner bow.
- Draw length — Longer draws create more dynamic flex. Longer arrows also need more spine.
- Arrow length — Longer arrows are effectively weaker (more leverage at the tip). Add 5 spine numbers per extra inch beyond 28".
- Point weight — Heavier points (100gr+) flex the arrow more. Add 25–50 spine for heavy field points or broadheads.
- Bow type — Compound bows with let-off require slightly weaker spine than recurves at the same draw weight.
Rough guide:
- 20–30 lb: 600–700 spine
- 30–40 lb: 500 spine
- 40–50 lb: 400–500 spine
- 50–60 lb: 340–400 spine
- 60–70 lb: 300–340 spine
- 70+ lb: 250–300 spine
Always check the manufacturer’s spine chart for your specific arrow brand, as ratings vary slightly. Fine-tune with paper tuning or bare-shaft tuning.