What is ballistic coefficient?

BC measures a projectile's ability to overcome air resistance. Higher BC → less drag → better long-range performance.

What is the difference between G1 and G7?

G1 uses a flat-base reference shape; G7 uses a boat-tail shape. Most modern rifle bullets are better described by G7.

What is sectional density?

SD is mass divided by cross-sectional area — it indicates penetration potential independent of shape.

How does altitude affect BC?

Lower air density at altitude reduces drag, effectively increasing the projectile's BC performance.

What BC is considered high?

For rifle bullets, BC > 0.5 (G1) is considered high; match-grade long-range bullets often exceed 0.6.

Spin stabilises the bullet and reduces yaw, keeping the effective drag coefficient close to its ideal value.

Ballistic Coefficient Calculator

Calculate ballistic coefficient, sectional density, drag force, and muzzle energy for projectiles. Compare G1/G7 models with built-in presets.

Projectile Presets

Projectile Mass (g)

Caliber / Diameter (mm)

Drag Coefficient (Cd)

Muzzle Velocity (m/s)

Air Density (kg/m³)

Drag Model

Ballistic Coefficient (SI)

504.89

kg/m² — higher BC means less drag deceleration

BC (Imperial)

0.037

lb/in² — standard in shooting sports

Sectional Density (SI)

198.42 kg/m²

Mass per unit cross-section area

Sectional Density (Imp)

0.014

lb/in² — critical for terminal performance

Drag Force at V₀

8.12 N

Aerodynamic drag at muzzle velocity

Deceleration

851.9 m/s²

86.8 g — initial drag deceleration

Form Factor (i)

0.757

Cd / G1 reference Cd — lower is more streamlined

Muzzle Energy

3,346 J

2,468 ft·lbf

BC Rating

Projectile Comparison

Projectile	Mass (g)	Dia (mm)	Cd	BC (Imp)
5.56 NATO 62 gr	4.02	5.69	0.295	0.039
7.62 NATO 147 gr	9.53	7.82	0.393	0.037
.50 BMG 660 gr	42.77	12.95	0.365	0.064
9 mm 115 gr	7.45	9.01	0.165	0.051
.308 Win 168 gr	10.89	7.82	0.462	0.036
Baseball	145	73.5	0.3	0.008

Velocity Decay Estimate

Range (m)	Est. Velocity (m/s)	Energy (J)	Drop Factor
0	838.0	3,346	1.000
100	760.7	2,757	0.908
200	696.4	2,311	0.831
300	642.2	1,965	0.766
500	555.6	1,471	0.663
800	462.1	1,018	0.551

Planning notes, formulas, and examples

About the Ballistic Coefficient Calculator

The **Ballistic Coefficient Calculator** quantifies how well a projectile overcomes air resistance. A higher ballistic coefficient (BC) means the projectile retains velocity and energy better over distance — a critical metric for long-range shooting, ammunition selection, and aerodynamic engineering.

BC is defined as the ratio of sectional density to drag coefficient, and it depends on the projectile's mass, caliber, and aerodynamic shape. This calculator gives you BC in both SI (kg/m²) and traditional imperial (lb/in²) units, plus sectional density, form factor, drag force, deceleration, and muzzle energy. Choose from common projectile presets or enter custom values.

Whether you are comparing ammunition, designing a projectile, or studying external ballistics, the built-in comparison table and velocity-decay estimates give you actionable data. Support for both G1 (flat-base) and G7 (boat-tail) drag models ensures the results align with modern ballistic software.

When This Page Helps

Choosing ammunition or designing projectiles without understanding BC leads to inaccurate range estimations. It gives ballistic data for any projectile, saving time and enabling informed comparisons.

How to Use the Inputs

Select a projectile preset or enter custom mass, diameter, and drag coefficient.
Set the muzzle velocity in m/s.
Enter air density (default 1.225 kg/m³ at sea level, 15 °C).
Choose the drag model (G1 for flat-base bullets, G7 for boat-tail).
Read the ballistic coefficient, sectional density, drag force, and muzzle energy.
Use the comparison and velocity-decay tables for range planning.

Formula used

BC = m / (Cd × A)
Sectional Density: SD = m / A
Drag Force: F_d = ½ ρ v² Cd A
Form Factor: i = Cd / Cd_ref (G1 ref = 0.5191)
Muzzle Energy: KE = ½ m v²

where m = mass, A = cross-section area, Cd = drag coefficient, ρ = air density, v = velocity.

Example Calculation

Result: BC ≈ 0.505 (SI), 0.393 (imperial), muzzle energy 3 346 J

A 147-grain 7.62 NATO round with Cd 0.393 has a moderate BC of about 0.39 imperial, retaining energy well out to 500 m.

Tips & Best Practices

A heavier bullet of the same caliber always has higher sectional density.
Boat-tail bullets have lower Cd and higher BC — prefer them for long range.
Temperature and altitude both change air density; adjust accordingly.
Form factor < 1 means the bullet is more streamlined than the G1 reference.
Use the velocity-decay table to determine effective range.

When To Use This Calculator

Calculate ballistic coefficient, sectional density, drag force, and muzzle energy for projectiles. Compare G1/G7 models with built-in presets. Use it when you need a repeatable calculation in the physics / general category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.

How To Check The Result

Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.

Practical Notes

Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.

Sources & Methodology

Last updated: January 15, 2025

Frequently Asked Questions

BC measures a projectile's ability to overcome air resistance. Higher BC → less drag → better long-range performance.