How this calculator works
This is the dimensional physics definition of ballistic coefficient. Combining it with quadratic drag shows that deceleration at a given fluid density and speed decreases as this coefficient increases. Use projected area perpendicular to the flow and a drag coefficient based on that same area. A constant drag coefficient is an approximation, especially across changes in Mach or Reynolds number.
Formula
B = m/(Cd A); drag acceleration magnitude = rho v^2/(2B). B has units kg/m2.
Worked example
For a 2 kg body with Cd = 0.4 and area 0.5 m2, B = 10 kg/m2. A 3 kg body with B = 20 kg/m2 and Cd = 0.5 has area 0.3 m2.
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Frequently asked questions
Is this a G1 or G7 coefficient?
No. G1 and G7 compare a projectile with standard drag models. Their conventional coefficients are not interchangeable with this SI definition.
Does a larger value mean less deceleration?
At equal fluid density and speed, yes, within the same quadratic-drag model.
Which area belongs here?
Use frontal projected area, consistent with the reference area used to define Cd.