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 of an arrow shaft, meaning how much it flexes when shot. Getting the right spine is one of the most critical factors in archery accuracy. An arrow that is too stiff (over-spined) or too weak (under-spined) will not fly straight and groups go to pieces.
How spine is measured (AMO/ATA method): A 28-inch arrow is supported at two points 26 inches apart, and a 1.94 lb (880g) weight is hung from the center. The deflection in inches × 1000 = the spine number. A 0.400-inch deflection = 400 spine.
Lower spine number = stiffer arrow
- 300 spine: very stiff (heavy draw weights)
- 400 spine: medium stiff
- 500 spine: medium flex
- 600 spine: flexible (light draw weights)
Common spine numbers by draw weight:
| Spine | Draw Weight Range | Typical Use |
|---|---|---|
| 250–300 | 65–80 lbs | Heavy compound, hunting |
| 340–350 | 55–70 lbs | Mid-weight compound |
| 400 | 45–60 lbs | Standard compound or recurve |
| 500 | 35–50 lbs | Recurve, lighter compound |
| 600 | 25–40 lbs | Light recurve, youth bows |
| 700–900 | Under 30 lbs | Youth, beginner recurve |
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 are also 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 about 25 spine points per 25 extra grains beyond 100gr.
- Bow type. Compound bows with let-off require slightly weaker spine than recurves at the same draw weight.
Compound vs recurve:
- Compound bows: Use the actual peak draw weight for spine selection.
- Recurve and traditional bows: Use the draw weight AT YOUR draw length, not the bow’s rated weight. Most recurves are rated at 28" draw. If you draw shorter or longer, adjust accordingly (roughly 2.5 lb per inch off rated).
Arrow length: A properly fitted arrow should extend 1–2 inches past the rest at full draw. Arrows that are too short are a safety hazard.
The “weak side” rule: If in doubt, pick a slightly weaker spine (higher number) rather than one that is too stiff. A slightly weak spine is more forgiving than overspine, which throws nocks left for right-handed shooters.
Always check the manufacturer’s spine chart for your specific arrow brand. Ratings vary slightly between Easton, Gold Tip, Black Eagle, and Victory. Fine-tune with paper tuning or bare-shaft tuning after a starting recommendation.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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