Spring, Barrel & BB → Velocity & Joules Calculator
This calculator predicts muzzle velocity (FPS) and energy (Joules) from your airsoft setup. By selecting barrel length, spring strength, and BB weight, you get an estimated performance output. It’s a useful tool for airsoft techs and players planning custom builds, giving a baseline idea of how changes in setup affect FPS and energy before hitting the chrono. Always verify with a chronograph for official field compliance.
Airsoft Velocity & Energy Estimator
Estimate muzzle velocity and energy from barrel length, spring rating, and BB weight. Results are approximate—chrono your setup for field limits.
Reference: 300 mm. Longer barrels give diminishing returns if cylinder volume is matched.
Approx base: 380 fps @ 0.20 g, ~300 mm
Common: 0.20–0.32 g (outdoor often 0.28–0.32 g).
Estimated velocity
0.0 fps
0.00 m/s
Estimated energy
0.000 J
at muzzle
Assumptions
Base map is typical FPS with 0.20 g at ~300 mm; energy scaled by barrel length; velocity derived from E = ½·m·v².
How it works (math)
1) Convert the base spring FPS (with 0.20 g @ 300 mm) to Joules:
2) Adjust for barrel length with a bounded factor:
3) Convert energy back to velocity for your BB mass:
E₀ = ½·m·v².2) Adjust for barrel length with a bounded factor:
E = E₀ · (1 + a·tanh((L − 300)/b)), with a = 0.06, b = 200.3) Convert energy back to velocity for your BB mass:
v = √(2E/m).