The ballistic coefficient (BC) measures how well a projectile keeps its speed in flight. A high BC – heavy, narrow and streamlined – means less drag deceleration, a flatter trajectory and less wind drift. It is used for bullets, artillery, skydivers and re-entering spacecraft.
How to use the Ballistic Coefficient Calculator
- Mass of projectile
- Cross-sectional area
- Drag coefficient C_d
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
The mass is divided by the product of the drag coefficient and the frontal area. A larger value means the projectile is less affected by drag. The result is shown in kg/m² and in the lb/in² form used by ammunition makers (without their reference-projectile form factor).
Inputs explained
| Field | What to enter |
|---|---|
| Mass of projectile | Units: g, kg, mg, lb, oz, gr |
| Cross-sectional area | Units: cm², mm², m², in² |
| Drag coefficient C_d | A number |
Example values
How the main result changes when Mass of projectile changes and everything else stays at the example values above:
| Mass of projectile (g) | Ballistic coefficient (kg/m²) |
|---|---|
| 0.005 | 0.3333 |
| 0.0075 | 0.5 |
| 0.01 | 0.6667 |
| 0.0125 | 0.8333 |
| 0.015 | 1 |
| 0.02 | 1.3333 |
Formula
BC = m / (C_d × A)
Worked example
Inputs — Mass of projectile: 0.01 g; Cross-sectional area: 0.5 cm²; Drag coefficient C_d: 0.3.
Results — Ballistic coefficient = 0.6667 kg/m².
Key terms
- Drag coefficient
- A dimensionless number describing how streamlined a shape is.
Frequently asked questions
What is a good ballistic coefficient for a bullet?
Rifle bullets typically range from about 0.2 to 0.7 (lb/in², G1 model).
Why does a heavier bullet have a higher BC?
More mass per unit of frontal area resists drag deceleration better.
Is BC constant during flight?
No – it changes with speed, especially near the speed of sound.
What is the G1 standard?
A reference projectile shape used to express bullet BCs relative to a standard drag curve.