The muzzle velocity is the most common value given in airsoft replicas and tells us how fast the ball is flying. The value is given in FPS (Feet per Second) or m/s (meters per second). An alternative indication of the gun's power can be by the force of the ball given in joules (J)

As a usually rule, all dealer and manufacturer values are measured at 0.20g. 

Conversion:

• 1 FPS = 0.3 m/s
• 1 J = 99 m/s
• 1 J = 326.7 FPS