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 two different reference projectile shapes used to build drag models. G1 (flat-base spitzer) is the traditional American standard; G7 (boat-tail) matches modern long-range rifle bullets more closely. This calculator computes the physical BC from first principles — the result in lb/in² is equivalent to a G1-referenced BC only when Cd matches the G1 drag model.

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

Name: Ballistic Coefficient Calculator
Availability: InStock
Author: Nham Vu

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

Enter projectile mass, diameter, and drag coefficient to compute the ballistic coefficient in lb/in² or 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.
Convert between G1 form-factor BC and raw physical BC.
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