Arrow spine measures how much an arrow shaft flexes under load. The spine number (e.g., 400, 500) refers to static spine — the deflection in thousandths of an inch when a 1.94 lb weight is hung at the center of a 28″ span. Too stiff a spine causes the arrow to fly left (for right‑handed archers); too weak can cause erratic flight or even dangerous contact with the bow. This tool uses your draw weight, arrow length, and point weight to recommend a spine that tunes correctly.

Higher draw weight applies more force to the arrow, requiring a stiffer shaft (smaller spine number). For example, a 50 lb recurve bow typically needs a spine around 400, while a 70 lb bow may need a 300 spine.

Longer arrows are more flexible than shorter ones of the same material. To maintain proper flex during release, a longer arrow needs a stiffer static spine. Our calculator adjusts the base spine up or down by approximately 5–10 spine units per inch of length above or below 28″.

Heavier points (broadheads or field tips) increase the effective load on the arrow during acceleration, demanding a slightly stiffer spine. The tool adds a correction of about 5–10 spine units per 25 grains above or below 100 grains.

Compound bows impart energy more efficiently and accelerate arrows faster, so they typically require a slightly stiffer spine than a recurve of the same draw weight. Our selector applies a separate baseline chart for each bow type.