Ballistic Coefficient Calculator

Ballistic coefficient is a compact way to compare how efficiently projectiles overcome aerodynamic drag relative to a standard reference projectile. A higher coefficient generally indicates that a bullet retains velocity and energy better and experiences less wind drift over the same flight conditions. It does not describe muzzle velocity, precision, terminal behavior, or suitability by itself. The value only has meaning when it is paired with the drag model and velocity range used to define the form factor. The calculation begins with sectional density, which is projectile weight in pounds divided by diameter in inches squared. Because bullet weights are commonly listed in grains, this calculator divides grains by 7,000 to convert them to pounds before applying the formula. Sectional density expresses how much mass is concentrated behind a given frontal area. Long, heavy-for-caliber bullets usually have greater sectional density than short, light bullets of the same diameter. Ballistic coefficient equals sectional density divided by form factor. The form factor compares the bullet's drag with the standard projectile for a selected model. A value below one means the projectile shape produces less drag than that reference at the modeled conditions, while a value above one means more drag. G1 and G7 references have different standard shapes, so a G1 coefficient and a G7 coefficient for the same bullet are not interchangeable. Always use the form factor, coefficient, and trajectory solver for the same drag model. Published coefficients are often measured over a velocity band rather than derived solely from geometry. Drag changes through supersonic, transonic, and subsonic flight, and modern manufacturers may publish multiple banded values or a custom drag curve. This calculator is therefore best for understanding the relationship among mass, caliber, form factor, sectional density, and coefficient, or for checking a value when an appropriate form factor is known. For actual trajectory predictions, prefer Doppler-verified manufacturer data and confirm velocity with a chronograph. Atmospheric density, sight height, twist rate, muzzle velocity, and wind must be handled by a complete ballistic solver, and safe load development must always follow reliable published data.