Ballistic Coefficient
Calculate ballistic coefficient from bullet weight, caliber diameter, and G1 drag coefficient. Free tool for shooters, hunters, and ballisticians.
About This Calculator
The Ballistic Coefficient (BC) Calculator computes the G1 ballistic coefficient and sectional density for any projectile given its weight in grains, caliber diameter in inches, and G1 drag coefficient. This tool is essential for shooters, hunters, ballisticians, and anyone involved in external ballistics who needs to estimate trajectory performance, wind drift, and velocity retention.
The calculator uses the standard G1 model formula: BC = (W / 7000) / (D² × C) where W is bullet weight in grains, D is caliber diameter in inches, and C is the G1 drag coefficient. The intermediate value SD = (W/7000) / D² is the sectional density. A higher ballistic coefficient means the bullet retains velocity better, drops less over distance, and is less affected by crosswinds — which is why high-BC match bullets are preferred for precision long-range shooting.
The ballistic coefficient also applies to other fields including aerospace engineering (re-entry vehicle design) and sports science (golf ball flight, baseball trajectory). The result is displayed in the standard unit of lbs/in², the convention used in shooting sports worldwide.
What the Results Mean
Ballistic Coefficient: The final BC value using the G1 standard. Typical range: 0.100 (pistol bullets) to 0.700+ (modern long-range match bullets). Sectional Density: The ratio of mass to cross-sectional area, indicating penetration potential independent of shape. These two metrics together help you compare different bullets for your specific shooting application.
Frequently Asked Questions
What is ballistic coefficient?
The ballistic coefficient (BC) is a measure of a projectile's ability to overcome air resistance during flight. It depends on the projectile's mass, cross-sectional area, and drag coefficient. A higher BC means the projectile retains velocity better and is less affected by crosswinds.
How is ballistic coefficient calculated?
The ballistic coefficient is calculated using the formula BC = (W/7000) / (D² × C) where W is bullet weight in grains, D is caliber diameter in inches, and C is the drag coefficient. The result is the sectional density (W/7000/D²) divided by the drag coefficient. This is the standard G1 model formula used in shooting sports.
What is the G1 drag model?
The G1 model is the most widely used standard drag model for ballistic coefficient calculations. It represents a flat-base, ogive-nose bullet shape. The G1 drag coefficient is typically around 0.519 for standard spitzer bullets. Other models (G2 through G7) exist for different projectile shapes, but G1 remains the most common in hunting and target shooting.
What is a good ballistic coefficient for a bullet?
Ballistic coefficients for common rifle bullets range from 0.200 to 0.700. A BC below 0.300 is considered low (typical of pistol bullets and some varmint rounds), 0.300-0.500 is moderate (standard hunting bullets), and above 0.500 is high (long-range match bullets). Higher BC bullets retain velocity better, drop less, and drift less in wind.
What is sectional density in ballistics?
Sectional density (SD) is the ratio of a bullet's mass to its cross-sectional area, calculated as SD = weight in pounds / caliber². For a given caliber, a heavier bullet has higher sectional density, which improves penetration. Sectional density is a key component of the ballistic coefficient formula.
How does drag coefficient affect ballistic coefficient?
The drag coefficient (Cd) measures how aerodynamic a projectile's shape is. A lower drag coefficient results in a higher ballistic coefficient because the BC formula divides by Cd. For example, a sleek spitzer boat-tail bullet might have a Cd of 0.4-0.5, while a round-nose bullet might have a Cd of 0.6-0.7, making the spitzer bullet have a significantly higher BC.
Can ballistic coefficient be used for long-range shooting?
Yes, ballistic coefficient is the most important factor for long-range shooting. A high BC bullet will drop less and drift less in wind at extended ranges. For example, a 6.5mm Creedmoor with a 140-grain bullet (BC ~0.650) has significantly less wind drift at 1000 yards than a .308 Winchester with a 168-grain bullet (BC ~0.460). This is why high-BC bullets are preferred for precision long-range shooting.
What is the difference between G1 and G7 ballistic coefficients?
The G1 model represents a flat-base spitzer bullet, while G7 represents a boattail spitzer bullet. G7 BC values are typically lower than G1 values for the same bullet, often by a factor of about 0.5-0.7. Modern long-range bullets with boattail designs are better modeled by the G7 standard, though G1 remains the most widely quoted specification.