Barrel Twist Rate Calculator

Calculate the required rifling twist rate for stabilize a projectile using the Greenhill Formula.

Input Parameters

Bullet Diameter (d) (inches)

Bullet Length (L) (inches)

Muzzle Velocity Category

Calculation Results

Enter bullet specs to calculate

About this calculator

Quick Reference

dBullet diameter

LBullet length

CConstant (150 or 180)

Overview

The Greenhill formula is a simple rule of thumb for calculating the optimum rifling twist for solid lead-alloy bullets.

💡

Pro Tips

Fun Facts

"Sir Alfred George Greenhill was a British mathematician who developed this formula in 1879."
"A '1 in 7' twist means the bullet completes one full rotation every 7 inches of barrel length."
"Heavier and longer bullets require a 'faster' twist (lower number) to remain stable in flight."

Formula: Twist = (C * d²) / L