Converter
FPS to Joules and Joules to FPS converter
Convert Joules to FPS (or the other way round) for any BB weight. Exact formula, instant result, with reference values for common field limits.
Joules to FPS by BB weight
Values use the exact formula. Your replica's power is usually measured with a reference BB, often 0.20 g.
| Energy | 0.20 g | 0.25 g | 0.28 g | 0.30 g | 0.36 g |
|---|---|---|---|---|---|
| 0.5 J | 232 | 207 | 196 | 189 | 173 |
| 0.8 J | 293 | 262 | 248 | 240 | 219 |
| 1.0 J | 328 | 293 | 277 | 268 | 245 |
| 1.2 J | 359 | 321 | 304 | 293 | 268 |
| 1.5 J | 402 | 359 | 340 | 328 | 299 |
| 2.0 J | 464 | 415 | 392 | 379 | 346 |
How to convert Joules to FPS
A chronograph shows a speed (FPS or m/s). Field rules set an energy in Joules. The conversion depends on BB weight: at the same speed, a heavier BB carries more energy.
The formula
E = ½ × m × v². With m in kg and v in m/s, E is in Joules. 1 FPS is 0.3048 m/s. To go from Joules to FPS, invert it: v = √(2E ÷ m), then divide by 0.3048.
Example at 0.20 g
300 FPS = 91.4 m/s = 0.84 J. 350 FPS = 106.7 m/s = 1.14 J. For 1.0 J you need about 328 FPS. For 1.5 J, about 402 FPS.
Why BB weight changes everything
At 1.0 J, a 0.25 g BB leaves at about 293 FPS, versus 328 FPS for a 0.20 g. A replica set to 1.0 J with 0.20 g goes over 1.0 J when you shoot heavier BBs (see joule creep).
Field limits
French regulation is based on muzzle energy, with a threshold at 2 J. Fields usually set lower limits, often around 1.2 J for assault rifles and 1.5 J for DMRs. Always check your field's rules.
What the conversion doesn't tell you
The formula assumes an exact BB mass and a reliable chronograph. Cheap BBs vary in weight, and a badly set chrono skews everything. Always measure with your own BBs.
Frequently asked questions
How many FPS is 1 Joule in airsoft?
With a 0.20 g BB, 1 Joule is about 328 FPS (100 m/s). With a 0.25 g BB, it is about 293 FPS.
How many Joules is 300 FPS?
300 FPS with a 0.20 g BB is about 0.84 Joule. With a 0.25 g BB, it is about 1.05 Joule.
How many Joules is 350 FPS?
350 FPS with a 0.20 g BB is about 1.14 Joule. With a 0.28 g BB, it is about 1.59 Joule.
What is the formula to convert FPS to Joules?
E = ½ × m × v², with m the BB mass in kg and v the speed in m/s. One FPS is 0.3048 m/s.
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