What is the ballistic coefficient?

The ballistic coefficient (BC) is a measure of a projectile's ability to overcome air resistance. It is defined as mass divided by the product of the drag coefficient and the cross-sectional area (BC = m / (Cd × A)). A higher BC means less deceleration due to drag — the projectile flies flatter and retains more velocity at distance.

What drag coefficient should I use?

The Cd depends on the projectile's shape and the velocity regime. Most ballistics software uses a form factor relative to a standard reference projectile (G1 or G7). For a rough physical BC, typical flat-base rifle bullets have Cd values between 0.30 and 0.55 at transonic speeds. Boat-tail bullets are usually 0.25–0.40. Pistol bullets are higher, around 0.45–0.70.

What is the difference between G1 and G7 BC?

G1 and G7 refer to standard reference projectile shapes used in small-arms shooting ballistics (G1 for flat-base spitzers, G7 for boat-tails). Commercial small-arms BCs are computed as sectional density divided by a form factor (m / (d² × i)), using caliber squared without the π/4 factor found in cross-sectional area A. Because this tool calculates aerodynamic BC as m / (Cd × A), its lb/in² output is inherently higher by roughly 4/π (~27.3%) than a commercial G1 or G7 rating and cannot be used directly in rifle drop tables without conversion.

Why does a higher BC improve long-range accuracy?

A high BC projectile decelerates more slowly, so it arrives at the target with more velocity, less wind drift, and a flatter trajectory. Less velocity drop also means less drop compensation and smaller corrections for wind. This is why long-range competition shooters prefer heavy, streamlined, high-BC bullets.

How accurate is this calculator?

The calculator uses the exact physical formula BC = m / (Cd × A). Accuracy depends on how accurate your Cd input is. Cd varies with velocity (Mach number), so the BC from a single Cd value is an approximation at one speed regime. For trajectory simulation, use a full drag model (G1/G7 tables). This tool is best for design comparison, sanity-checking, and education.

Ballistic Coefficient Calculator

Enter projectile mass, diameter, and drag coefficient to compute the ballistic coefficient in lb/in² or kg/m².

Projectile Parameters

Unit System

Projectile Mass

Grains (gr) — standard for bullets

Projectile Diameter

Caliber in inches (e.g. 0.308 for .308 Win)

Drag Coefficient (C_d)

Typical rifle bullets: 0.25–0.55 · Pistol: 0.45–0.70

Enter projectile parameters and click Calculate BC

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Summary

The ballistic coefficient (BC) measures how efficiently a projectile overcomes air resistance during flight. A higher BC means less drag relative to inertia — the projectile retains velocity better over distance. BC here is computed as aerodynamic ballistic coefficient: mass divided by the product of drag coefficient and cross-sectional area (m / (Cd × A)). Note that this physical aerodynamic BC differs from commercial small-arms shooting BC (m / (d² × i)), which uses caliber squared rather than area. This calculator accepts inputs in both imperial and metric units and outputs aerodynamic BC in lb/in² and kg/m².

How it works

Enter the projectile mass in grains (imperial) or grams (metric).
Enter the projectile diameter — the calculator derives cross-sectional area from it.
Enter the drag coefficient (Cd). For standard G1 reference, typical rifle bullets use Cd ≈ 0.30–0.55.
Select your preferred unit system (imperial or metric).
The calculator computes BC = mass / (Cd × cross-sectional area) and displays both unit formats.
Results update instantly as you change any input.

Use cases

Compare ballistic performance of different bullet designs.
Estimate retained velocity at long range for hunting or competition.
Validate manufacturer-published BC figures against physical dimensions.
Calculate aerodynamic deceleration metrics for re-entry and exterior ballistics modeling.
Assess how bullet diameter changes affect downrange performance.
Support external ballistics modeling and trajectory software.
Academic coursework on aerodynamics and projectile flight.
Evaluate custom cast or machined projectile designs.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu

Ballistic Coefficient Calculator

Projectile Parameters

Ballistic Coefficient

Derived Values

Performance Band

Summary

How it works

Use cases

Frequently Asked Questions

Ballistic Coefficient Calculator

Use the Ballistic Coefficient Calculator

Projectile Parameters

Ballistic Coefficient

Derived Values

Performance Band

Summary

How it works

Use cases

Frequently Asked Questions