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Arrow Spine Calculator

Calculate correct arrow spine deflection from draw weight, length, and point weight. Select properly spined arrows for recurve and compound bows.

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Inputs that matter
Draw Weight, Arrow Length, Point Weight, Nominal Spine (optional)
Output to expect
Arrow Spine Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Static Spine Measurement

Static spine is the deflection in inches when a 1.94 lb weight hangs from center of a 28-inch supported arrow. Lower deflection number = stiffer arrow (e.g., 340 spine is stiffer than 500).

Spine rating = deflection × 1000 / arrow length factor

Draw Weight Effect

Higher draw weight requires stiffer (lower spine number) arrows. Compound bows with high let-off and aggressive cams may need spine adjustment from traditional charts.

Peak draw weight → base spine from manufacturer chart

Point Weight Correction

Heavier broadheads and field points flex the arrow more at launch, requiring stiffer spine. Add ~5 spine units (stiffer) per 25 grains above 100 gr reference point.

Adjust 1 spine step stiffer per ~25 gr point weight increase

Updated: July 2026

Example Scenarios

Chart recommends 340 spine carbon arrow. At 29-inch length, drop to 300 spine (stiffer). With 125 gr broadhead, stiffen further to 300 or 250 spine.

40 lb recurve, 31-inch arrow, 120 gr point: select 500–550 spine aluminum or 400–450 carbon per Easton chart. Finger release adds slight side load vs release aid.

Light draw needs weak spine: 600–700 spine carbon at 26 inches with 85 gr point. Overspined arrows fly left (right-hand bow); underspined fly right.

Common Mistakes to Avoid

Using marked draw weight instead of actual peak weight

Measure peak draw weight with a scale on your specific bow setup. Limbs rated 50 lb may pull 52 lb at your draw length — spine charts need actual measured weight.

Ignoring point weight when selecting spine

A 150 gr broadhead requires a stiffer spine than 100 gr field point at the same draw weight. Always include total point weight (insert + tip) in spine calculation.

FAQ

Arrow flexes excessively at release, causing inconsistent flight — typically groups wide or fishtails. Right-handed shooter sees arrows impact right of aim on compound bows.

Insufficient flex fails to clear the bow cleanly. Arrows may group left (RH shooter) and feel harsh. Less common problem than underspined but still reduces accuracy.

Yes. Longer arrows are effectively weaker (more flex). Cut 1 inch shorter = effectively stiffer by ~10–15 spine units. Always select spine for actual finished arrow length.

Compound with release aid allows slightly weaker spine than finger shooting at same weight because release is cleaner. Finger shooters need ~5% stiffer spine typically.

Spine numbers are standardized by deflection measurement, but manufacturing tolerance varies. Easton 340 and Gold Tip 340 should be similar — verify with bare shaft tuning.

About Arrow Spine Calculator

Arrow spine — stiffness under load — must match bow draw weight, arrow length, and point weight for accurate flight. This calculator recommends spine deflection (static spine rating) for target and hunting setups.