Ballistic Coefficient Calculator
Calculate a projectile’s ballistic coefficient from its weight, diameter, and form factor, a measure of how well it resists air drag in flight.
What ballistic coefficient measures
Ballistic coefficient (BC) describes how efficiently a projectile overcomes air resistance in flight relative to a standard reference projectile shape. A higher BC means the projectile retains velocity better and drops less over distance, which matters for long-range accuracy.
The formula
This calculator first computes sectional density, SD = W / (7000 Ć dĀ²), where W is bullet weight in grains and d is diameter in inches (7000 converts grains to pounds). Ballistic coefficient is then BC = SD / i, where i is the projectile’s form factor relative to a standard reference drag model (such as G1), with i = 1 meaning the projectile matches the reference shape’s drag exactly. Form factor is normally supplied by the manufacturer or derived from doppler radar testing.
This is a standard exterior-ballistics approximation for general reference and educational use. Actual trajectory also depends on altitude, air density, spin drift, and other factors not captured here.